Borazine-based resin, and method for production thereof, borazine based resin composition, insulating coating and method for formation thereof, and electronic parts having the insulating coating

ABSTRACT

Interlayer insulating films  5,7  (insulating films) provided in a memory capacitor cell  8  are formed between a gate electrode  3  and a counter electrode  8 C formed on a silicon wafer  1.  The interlayer insulating films  5,7  comprise a borazine-based resin, having a specific dielectric constant of no greater than 2.6, a Young&#39;s modulus of 5 GPa or greater and a leak current of no greater than 1×10 −8  A/cm 2 .

TECHNICAL FIELD

The present invention relates to a borazine-based resin and a processfor its production, and to a borazine-based resin composition, aninsulating film and a method for its formation.

BACKGROUND ART

The miniaturization, increased output and faster signal speeds ofcommunication devices in recent years have led to greater flattening offilms by CMP and increasing demands for greater heat resistance,mechanical properties, hygroscopicity, adhesion, moldability and highetching selection ratio, and particularly a low specific dielectricconstant, for the insulating films (IMD: intermetal dielectrics, ILD:interlayer dielectrics, PMD: premetal dielectrics, etc.) of electronicproducts.

Most particularly, the micronization of wirings due required forincreased integration of semiconductor electronic parts (devices) suchas LSIs and the like has been accompanied by problems such as longersignal delay times as a result of increased interwiring capacities, andtherefore efforts have been more actively directed toward achievinglower dielectric constants and shorter heat treatment steps, as well asgreater heat resistance and mechanical properties of electronic partinsulating materials.

This is because, generally speaking, the wiring signal propagation speed(v) and the specific dielectric constant (ε) of an insulating materialin contact with a wiring material are in the relationship represented byv=k/√ε) (where k is a constant), and therefore in order to increase thesignal propagation speed to reduce the wiring delay it is necessary toeither increase the frequency range used or absolutely minimize thespecific dielectric constant of the insulating material.

Low dielectric constant materials currently being implemented as suchinsulating film materials for mass production include SiOF films (byCVD) having specific dielectric constants of about 3.5, while organicpolymers such as organic SOG (Spin On Glass) having specific dielectricconstants of 2.6-3.0 are also being investigated. Porous materials withpores in the films have also been proposed as insulating film materialswith even lower specific dielectric constants of less than 2.6, andresearch is actively progressing towards their application for LSIinterlayer insulating films.

Another low dielectric constant material is borazine, having a molecularstructure wherein benzene carbon atoms are replaced with nitrogen atomsand boron atoms, which is known to have a lower calculated dielectricconstant than benzene. Borazine-containing silicon polymer thin-filmsare also known to have high heat resistance.

DISCLOSURE OF THE INVENTION

Still, insulating films having low dielectric constants achieved byconventional pore formation tend to also exhibit lower film strengthwith lower dielectric constant, and when such films are flattened by,for example, CMP (Chemical Mechanical Polishing), major inconveniencessuch as film peeling occur more readily, while the process adaptabilityand the reliability of the devices using the insulating films areimpaired.

In addition, since a borazine-containing silicon polymer thin-film isproduced by simple coating of a solution comprising a mixture of aB,B′,B″-trialkynylborazine compound and a hydrosilyl group-containingsilicon compound in the presence of a platinum catalyst, the platinumcatalyst remains as an unavoidable impurity in the thin-film. Metallicimpurities in an interlayer insulating film can cause leak current andreduce or impair the performance of the insulating film. It is thereforeeasy to imagine that when a borazine-containing silicon polymerthin-film is used as an interlayer insulating film, the platinumcatalyst will act as a metallic impurity to produce leak current.

Materials applied for LSI interlayer insulating films must exhibit a lowdielectric constant as well as excellent heat resistance and highadhesion. CMP is essential for global flattening in multilayer wiringprocesses for ultraminiature next-generation LSIs, and adhesion is anespecially important factor for increasing the polishing resistance forCMP.

Yet, the aforementioned organic SOG, organic polymers and porousmaterials which are considered effective as low dielectric constantmaterials having specific dielectric constants of 3.0 or lower, whilehaving lower dielectric constants than conventional SiO₂ films or SiOFfilms formed by CVD, also tend to have insufficient adhesion for upperlayer films such as hard masks, which are required for trench (groove)working during wiring formation. Thus, easy peeling between upper layerfilms and insulating films composed of such low dielectric constantmaterials has been a problem in CMP processes, and consequently therehas been a strong desire for improvement in the adhesion of lowdielectric constant materials.

The present invention has been accomplished in light of thecircumstances described above, and one of its objects is to provide aninsulating film with adequately increased mechanical strength andelectrical properties, as well as electronic parts which effectivelyprevent wiring delay while exhibiting mechanical strength and improvedreliability.

It is another object of the invention to provide an insulating filmhaving low metallic impurities and adequately minimized generation ofleak current, as well as a process for its manufacture, a borazine-basedresin composition that can be used to effectively form the insulatingfilm, and a borazine-based resin as the main component of theborazine-based resin composition, as well as a process for itsproduction. It is yet another object of the invention to provideelectronic parts with minimal generation of leak current and adequateresistance to reduction or impairment of characteristics.

In order to achieve the objects stated above, the insulating film of theinvention (hereinafter referred to as “insulating film A”) ischaracterized by comprising in its molecular structure a compound havinga borazine skeleton (hereinafter referred to as “borazine compound”),and by having a specific dielectric constant of no greater than 2.6, aYoung's modulus of 5 GPa or greater and a leak current of no greaterthan 1×10⁻⁸ A/cm².

The insulating film A having this construction has a specific dielectricconstant of no greater than 2.6, but does not require pore formation forsuch a low specific dielectric constant as is the case with conventionalorganic polymers. The reduction in film strength which occurs with poreformation can therefore be avoided. The insulating film A also has aYoung's modulus of 5 GPa or greater, and the film therefore exhibitsexcellent mechanical properties and is highly suitable for flatteningsteps when the insulating film is used as in interlayer insulating film.In addition, the leak current of no greater than 1×10⁻⁸ A/cm² makes itpossible to eliminate the risk of impaired device characteristics whenthe insulating film A is used as an interlayer insulating film, forexample.

The insulating film A of the invention is preferably formed from aborazine-based resin composition with a metal impurity content of nogreater than 30 ppm. If the metal impurity content of the borazine-basedresin composition as the starting material is greater than 30 ppm, theinsulating film of the invention may not be able to exhibit the requiredlow specific dielectric constant, or the leak current may becomesignificant, when it is used as an interlayer insulating film of amultilayer wiring in an ultraminiature structure, for example.

An electronic part according to the invention (hereinafter referred toas “electronic part A”) is any electronic device such as a semiconductordevice or liquid crystal device which is constructed using an insulatingfilm according to the invention, or in other words, one provided with aconductive layer-formed substrate and an interlayer insulating filmformed on the substrate and composed of an insulating film according tothe invention.

A composite insulating film according to the invention (“hereinafterreferred to simply as “composite insulating film”) is one provided witha first insulating film comprising a siloxane resin (polysiloxane) and asecond insulating film formed on the first insulating film andcomprising a compound having a borazine skeleton in the molecularstructure (a borazine compound).

Since the first insulating film in a composite insulating film havingsuch a structure comprises a siloxane resin, it is easy to introducepores into the film during formation of the resin from the startingsolution, thereby allowing low dielectric constant to be achieved bypore formation. In addition, since the second insulating film formedthereover comprises a borazine skeleton in the molecular structure, itis possible to achieve a low dielectric constant for the film andtherefore a lower dielectric constant for the composite insulating filmas a whole. Moreover, since the dielectric constant of the secondinsulating film can be lower than the dielectric constant of the firstinsulating film, there is no need for excessive pore formation in thefirst insulating film. Consequently, the mechanical strength of thefirst insulating film, and therefore the composite insulating film as awhole, can be increased.

The second insulating film which comprises a borazine compound adheresvery well to other layers, or in other words, it has very excellentadhesion with other layers. In a composite insulating film of theinvention, the second insulating film which exhibits high adhesion isformed over the first insulating film, so that when an upper layer filmsuch as a hard mask is formed on the composite insulating film, theupper layer film adheres to the second insulating film and forms astrong bond between them. A strong bond is also formed between the firstinsulating film and the second insulating film. Thus, the adhesioninside the composite insulating film and between the compositeinsulating film and upper layer film is increased, thereby helping toprevent layer peeling during CMP and other steps.

Specifically, the first insulating film is preferably one composed of asiloxane resin composition comprising a siloxane resin obtained byhydrolytic condensation of a compound represented by the followingformula (1).X¹ _(n)SiX² _(4-n)   (1)In this formula, X¹ represents an H atom, an F atom, a group containinga B atom, N atom, Al atom, P atom, Si atom, Ge atom or Ti atom, or anorganic group of 1 to 20 carbons, X² represents a hydrolyzable group,and n represents an integer of 0-2, with the proviso that when n is 2,each X¹ may be the same or different, and when n is 0-2, each X² may bethe same or different.

The starting material for the first insulating film can be easilyprepared as a solution by dissolving the compound represented by formula(1) in a solvent, and this may be coated and then heated to causehydrolytic condensation and produce a siloxane resin while thermosettingit, thereby allowing the first insulating film to be easily formed. If aporous material, or a component which volatilizes at a lower temperaturethan the thermosetting temperature is added to the starting material, itwill be possible to easily form fine pores in the first insulating film.If a component which aids dehydrating condensation reaction of thecompound represented by formula (1) is added, it will be possible toreduce the Si—OH bonds and increase the density of siloxane bonds, whilealso promoting relaxation of stress in the first insulating film due tothe higher densification of siloxane bonds and the annealing effect ofthermosetting.

The borazine compound is preferably one having a repeating unitrepresented by the following formulas (2):

from the standpoint of the film forming property and chemical stability.

In these formulas, R¹ represents alkyl, aryl, aralkyl or hydrogen, R²represents alkyl, aryl, aralkyl or hydrogen, R³ and R⁴ representidentical or different monovalent groups selected from among alkyl,aryl, aralkyl and hydrogen, R⁵ represents a substituted or unsubstitutedaromatic divalent group, an oxypoly(dimethylsiloxy) group or oxygen, R⁶represents alkyl, aryl, aralkyl or hydrogen, a represents a positiveinteger, b represents 0 or a positive integer, p represents 0 or apositive integer, and q represents 0 or a positive integer.

Another electronic part according to the invention (hereinafter referredto as “electronic part B”) comprises a composite insulating film of theinvention on a substrate such as a silicon wafer. Also useful is alaminate (structure) wherein another upper film, such as a hard mask,anti-reflection (AR) film, reflection film, resist film or the likecovers the second insulating film which contains a borazine skeleton inthe molecular structure. Particularly useful are laminated bodieswherein the upper layer film is a hard mask, which is necessary forformation of the metal wiring pattern on the insulating film and whichrequires firm adhesion.

One process for production of a borazine-based resin according to theinvention (hereinafter referred to as “first borazine-based resinproduction process”) is a process for production of a borazine-basedresin that is a polymer having a borazine skeleton on the main chain ora side chain (hereinafter referred to simply as “borazine-based resin”),the process being characterized by comprising a first step ofpolymerizing a B,B′,B″-trialkynylborazine and a hydrosilane in thepresence of a solid catalyst, and a second step of removing the solidcatalyst after completing the first step.

In the first step of the first borazine-based resin production process,the B,B′,B″-trialkynylborazine and hydrosilane are polymerized to form aborazine-based resin which is a borazine-containing silicon-basedpolymer, but since a solid catalyst is used as the catalyst, thecatalyst can be very easily removed in the second step, with a low rateof residue. It is therefore possible to obtain a borazine-based resinwith the metal component adequately eliminated.

The solid catalyst is preferably a supporting catalyst with the catalystsupported on a compound-based carrier. Using this type of catalyst willrender filtration of the catalyst from the reaction system easier thanwhen using a supporting catalyst having the catalyst supported on anon-compound-based carrier (for example, a platinum-carbon catalyst), inwhich it is difficult to increase the catalyst particle size, so thatmetallic impurities can be drastically reduced. It will also eliminatethe risk of leak current resulting from conductivity of the carrier, aconcern with catalysts which are supported on carbon-based carriers (forexample, platinum-carbon catalysts).

Another process for production of a borazine-based resin according tothe invention (hereinafter referred to as “first borazine-based resinproduction process”) is a process for production of a borazine-basedresin that is a polymer having a borazine skeleton on the main chain ora side chain (borazine-based resin), the process being characterized bycomprising a first step of polymerizing a B,B′,B″-trialkynylborazine anda hydrosilane in the presence of a metal catalyst in a polymerizationsolvent, a second step of adding to the polymerization system (polymersolution) a particulate scavenger which is insoluble in thepolymerization system (polymer solution) of the first step and adsorbsthe metal component from the metal catalyst, after completion of thefirst step, and a third step of filtering out the scavenger to which themetal component has been adsorbed after completion of the second step.

In the first step of the second borazine-based resin production process,the B,B′,B″-trialkynylborazine and hydrosilane are polymerized to form aborazine-based resin. At this point, the metal component of the metalcatalyst still remains in the polymerization system (polymer solution),but addition of the particulate scavenger in the second step allows itsseparation and removal from the polymer solution. The scavenger ontowhich the metal component has adsorbed is particulate and insoluble inthe polymer solution and can therefore be easily filtered out in thethird step. This process yields a borazine-based resin from which themetal component has been adequately eliminated.

Using this type of scavenger allows the catalyst to be effectivelyrecovered even when a homogeneous catalyst is used as the metalcatalyst. Thus, a small amount of a homogeneous catalyst with highreactivity may be used for efficient reaction, and then recovered foreasy reuse of the catalyst, thereby improving economy and promotingeffective utilization of resources.

For the first and second borazine-based resin production processes, theB,B′,B″-trialkynylborazine is preferably one represented by thefollowing formula (3).

In this formula, R¹ represents alkyl, aryl, aralkyl or hydrogen, and R²represents alkyl, aryl, aralkyl or hydrogen.

More specifically, it is useful if the hydrosilane is one represented bythe following formula (4):

or the following formula (5).

In these formulas, R³ and R⁴ represent identical or different monovalentgroups selected from among alkyl, aryl, aralkyl and hydrogen, R⁵represents a substituted or unsubstituted aromatic divalent group, anoxypoly(dimethylsiloxy) group or oxygen, R⁶ represents alkyl, aryl,aralkyl or hydrogen, and n represents an integer of 2 or greater.

A borazine-based resin composition of the invention is characterized bycomprising a polymer with a borazine skeleton on the main chain or aside chain, and a solvent capable of dissolving the polymer, and byhaving a solid concentration of 0.5 wt % or greater (preferably with anupper limit of 80 wt %) and a metal impurity content of no greater than30 ppm.

The polymer is preferably a borazine-based resin produced by the firstor second borazine-based resin production process of the invention, inorder to exhibit a low specific dielectric constant and facilitatecoating onto bases such as semiconductor boards while dissolved in thesolvent.

If the solid concentration of the borazine-based resin composition isless than 0.5 wt %, the thickness of the film obtained by a singlecoating onto the substrate will be small, and the reliability of thefilm, including its strength and heat resistance, as well as itsinsulating property when dried as an insulating film, will be reduced.If the metal impurity content exceeds 30 ppm, it may not be possible toachieve the low specific dielectric constant required when theborazine-based resin composition is used, for example, as a multilayerwiring interlayer insulating film in an ultraminiature structure, or theleak current may become significant, potentially impairing theproperties of the element or other device. The “solid concentration”referred to here is the amount of residue components after drying offthe solvent and other volatile components of the resin composition.

According to the first and second borazine-based resin productionprocesses, the polymer preferably has a repeating unit represented bythe following formula (2):

from the standpoint of film forming property and chemical stability.

In these formulas, R¹ represents alkyl, aryl, aralkyl or hydrogen, R²represents alkyl aryl, aralkyl or hydrogen, R³ and R⁴ representidentical or different monovalent groups selected from among alkyl,aryl, aralkyl and hydrogen, R⁵ represents a substituted or unsubstitutedaromatic divalent group, an oxypoly(dimethylsiloxy) group or oxygen, R⁶represents alkyl, aryl, aralkyl or hydrogen, a represents a positiveinteger, b represents 0 or a positive integer, p represents 0 or apositive integer, and q represents 0 or a positive integer.

The method of forming an insulating film according to the invention is amethod for forming an insulating film on a substrate, characterized inthat the borazine-based resin composition is coated onto a substrate toform a coated film, and the coated film is then dried.

An insulating film according to the invention is formed on a substrateby the method of forming an insulating film of the invention, and it isparticularly useful as a film formed between adjacent conductive layersamong a plurality of conductive layers formed on a substrate, or inother words, as an interlayer insulating film which requires asatisfactory degree of reduction in leak current.

Another electronic part according to the invention (hereinafter referredto as “electronic part C”) is an electronic part comprising aninsulating film according to the invention, and it is used to constructan electronic device such as a semiconductor device or liquid crystaldevice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing an example of acomposite insulating film according to the invention.

FIG. 2 is a schematic cross-sectional view showing a preferredembodiment of an electronic part according to the invention.

FIG. 3 is a graph showing a gas chromatogram of the reaction solutionimmediately after the start of polymerization in Example 3-1.

FIG. 4 is a graph showing a gas chromatogram of the reaction solutionafter 3 days of stirring from the start of polymerization in Example3-1.

FIG. 5 is a graph showing a GPC chart for the polymer obtained inExample 3-1.

FIG. 6 is a graph showing a gas chromatogram of the reaction solutionimmediately after start of polymerization in Example 4-1.

FIG. 7 is a graph showing a gas chromatogram of the reaction solutionafter 3 days of stirring from the start of polymerization in Example4-1.

FIG. 8 is a graph showing a GPC chart for the polymer obtained inExample 4-1.

FIG. 9 is a graph showing a GPC chart for the polymer obtained inExample 4-5.

BEST MODES FOR CARRYING OUT THE INVENTION

(Borazine Compounds and Borazine-Based Resins)

The insulating film A, i.e. the second insulating film in a compositeinsulating film, comprises a borazine compound, and the compound ispreferably the same type of resin as a borazine-based resin obtained bythe first and second borazine-based resin production processes.

The borazine-based resin may be a polymer having a substituted orunsubstituted borazine skeleton on the main chain or a side chain, andfor example, there may be mentioned the polymers described in ChemicalReview, Vol.90, pp.73-91(1990) and CHEMTECH, July 1994, pp.29-37.Specifically there are preferred polymers having at least one of thefollowing repeating units.

Here, R, R′ and R″ represent H, Me (—CH₃) or Ph (—C₆H₅), and drepresents an integer of 2 or greater.

Borazine-based resins having repeating units represented by thefollowing formulas (2) and (6) may be mentioned as even more preferredborazine-based resins, because of their excellent film forming propertyand chemical stability.

In formulas (2) and (6), the portion:

represents either of the following:

while the portion:

represents either of the following:

and the portion:

represents either of the following.

The dotted line in formula (2) means that a bond is formed with thecarbon of the alkynyl group of the borazine residue, and the dotted linein formula (6) means that a bond is formed with the carbon of thealkenyl group of the borazine residue.

In formulas (2) and (6), R¹ represents alkyl, aryl, aralkyl or hydrogen.The number of carbon atoms of the alkyl group is preferably 1-24 andmore preferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for group R¹ there may be mentioned alkyl groups such asmethyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such as phenyl,naphthyl and biphenyl, aralkyl groups such as benzyl and phenethyl, andhydrogen, among which methyl, ethyl, phenyl and hydrogen are especiallypreferred.

Also in formulas (2) and (6), R² represents alkyl, aryl, aralkyl orhydrogen, and the number of carbon atoms of the alkyl group ispreferably 1-24 and more preferably 1-12. The number of carbon atoms ofthe aryl group is preferably 6-20 and more preferably 6-10. The numberof carbon atoms of the aralkyl group is preferably 7-24 and morepreferably 7-12. More specifically, for group R² there may be mentionedalkyl groups such as methyl, ethyl, isopropyl, t-butyl and octyl, arylgroups such as phenyl, naphthyl, biphenyl and anthracenyl, aralkylgroups such as benzyl, phenethyl and fluorenyl, and hydrogen, amongwhich methyl, phenyl and hydrogen are especially preferred.

Also in formulas (2) and (6), R³ and R⁴ represent identical or differentmonovalent groups selected from among alkyl, aryl, aralkyl and hydrogen,among which alkyl, aryl and hydrogen are preferred. In this case, thenumber of carbon atoms of the alkyl group is preferably 1-24 and morepreferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for groups R³ and R⁴ there may be mentioned alkyl groupssuch as methyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such asphenyl, naphthyl and biphenyl, aralkyl groups such as benzyl andphenethyl, and hydrogen, among which methyl, phenyl and hydrogen areespecially preferred.

Also in formulas (2) and (6), R⁵ represents a substituted orunsubstituted aromatic divalent group, an oxypoly(dimethylsiloxy) groupor oxygen. In this case, the number of carbon atoms of the aromaticdivalent group is preferably 6-24 and more preferably 6-12. Aromaticdivalent groups include divalent aromatic hydrocarbon groups (arylene,etc.) and arylene groups containing hetero atoms such as oxygen asconnecting groups. As substituents to be bonded to the aromatic divalentgroup there may be mentioned alkyl, aryl and aralkyl. More specifically,for group R⁵ there may be mentioned arylene groups such as phenylene,naphthylene and biphenylene, substituted arylene groups such asdiphenylether, and oxygen, among which phenylene, diphenylether andoxygen are especially preferred.

Also in formulas (2) and (6), R⁶ represents alkyl, aryl or hydrogen. Inthis case, the number of carbon atoms of the alkyl group is preferably1-24 and more preferably 1-12. The number of carbon atoms of the arylgroup is preferably 6-20 and more preferably 6-10. The number of carbonatoms of the aralkyl group is preferably 7-24 and more preferably 7-12.More specifically, for group R⁶ there may be mentioned alkyl groups suchas methyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such asphenyl, naphthyl and biphenyl, and aralkyl. groups such as benzyl andphenethyl.

Also in formulas (2) and (6), a and b represent the numbers of each ofthe repeating units, where a is a positive integer of preferably1-20,000, more preferably 3-10,000 and more preferably 5-10,000. Also, bis 0 or a positive integer of preferably 0-1000 and more preferably0-100. However, a and b are in a component proportion, and are notlimited to any particular form of bonding state (block copolymerization,random copolymerization, etc.).

There is no particular restriction on the numerical ratio of a and b(a:b) in the copolymer, and a larger afb ratio, i.e. a greaterproportion of the chain-like structure in the polymer main chain, ispredicted to increase the solubility of the copolymer in the solvent andlower the melting point, thereby improving workability of the copolymer.On the other hand, a lower a/b ratio, i.e. a greater proportion of thecrosslinked structure in the polymer main chain, is predicted to improvethe heat resistance and combustion resistance of the copolymer. Thus,the optimum range for the a/b ratio of the copolymer may beappropriately selected so as to produce satisfactory workability, heatresistance and combustion resistance, depending on the purpose of use,or depending on the structures and combinations of the monomer units ofthe copolymer.

Also in formulas (2) and (6), p represents 0 or a positive integer and qrepresents 0 or a positive integer, and these are in the followingrelationship with n: p+q+2=n. The preferred range for p is 0-10, with1-8 being more preferred. The preferred range for q is also 0-10, with1-8 being more preferred.

Also in formulas (2) and (6), Z¹ is a divalent group represented by thefollowing formula (7):

or the following formula (8):

where Z¹ may consist of the structure of either (7) or (8) in the samemolecular chain, or it may include both structures in the same molecularchain. The symbols R³, R⁴, R⁵, R⁶, p and q in formulas (7) and (8) arethe same as described above.

The molecular weight of the borazine-based resin (Mn; number averagemolecular weight calculated using a calibration curve for standardpolystyrene, with measurement by gel permeation chromatography (GPC)) ispreferably 500 to 5 million and more preferably 1000 to 1 million. Ifthe molecular weight (Mn) is excessively low, such as below 500, theheat resistance and the mechanical properties of the insulating filmdescribed hereunder will tend to be inferior, and, for example,prebaking will be more difficult to achieve when the insulating film isused as an interlayer insulating film, while peeling will tend to occurwhen the film is flattened by CMP. In contrast, if the molecular weight(Mn) is excessively high, such as above 5 million, the workability ofthe insulating film may be impaired, making it difficult to control theshape of metal plug-forming viaholes formed of W, etc. in the insulatingfilm.

(Process for Production of Borazine Compounds for Insulating Film A andComposite Insulating Film)

A borazine-based resin represented by formula (2) can be produced bypolymerizing a B,B′,B″-trialkynylborazine and a hydrosilane in thepresence of a solid catalyst. The metal-containing catalyst ispreferably removed after the polymerization. Alternatively, it may beproduced by hydroborating polymerization of a B,B′,B″-trihydroborazineand a bis(alkynylsilane) in the presence of a catalyst.

As specific examples of B,B′,B″-trialkynylborazines there may bementioned B,B′,B″-triethynylborazine,B,B′,B″-triethynyl-N,N′,N″-trimethylborazine,B,B′,B″-tri(1-propynyl)borazine, B,B′,B″-triphenylethynylborazine,B,B′,B″-triphenylethynyl-N,N′,N″-trimethylborazine,B,B′,B″-triethynyl-N,N′,N″-triphenylborazine,B,B′,B″-triphenylethynyl-N,N′,N″-triphenylborazine,B,B′,B″-ethynyl-N,N′,N″-tribenzylborazine andB,B′,B″-tris(1-propynyl)-N,N′,N″-trimethylborazine, which may be usedalone or in combinations of two or more.

Hydrosilanes include bis(monohydrosilane)s, bis(dihydrosilane)s,bis(trihydrosilane)s and poly(hydrosilane)s. As specific examples theremay be mentioned m-bis(dimethylsilyl)benzene,p-bis(dimethylsilyl)benzene, 1,4-bis(dimethylsilyl)naphthalene,1,5-bis(dimethylsilyl)naphthalene, m-bis(methylethylsilyl)benzene,m-bis(methylphenylsilyl)benzene, p-bis(methyloctylsilyl)benzene,4,4′-bis(methylbenzylsilyl)biphenyl,4,4′-bis(methylphenethylsilyl)diphenylether, m-bis(methylsilyl)benzene,m-disilylbenzene, 1,1,3,3-tetramethyl-1,3-disiloxane,1,3,5,7-tetramethylcyclotetrasiloxane,1,3,5,7,9-pentamethylcyclopentasiloxane,1,3,5,7-tetraethylcyclotetrasiloxane, 1,3,5-triphenylcyclotrisiloxane,1,3,5,7-tetraphenylcyclotetrasiloxane and1,3,5,7-tetrabenzylcyclotetrasiloxane, which may be used alone or incombinations of two or more.

There are no particular restrictions on the metal-containing catalyst tobe used for production of the borazine-based resin, and there may bementioned homogeneous metal-containing catalysts or heterogeneousmetal-containing catalysts commonly used for hydrosilylation ofacetylenes or olefins. Among these, heterogeneous metal-containingcatalysts are particularly preferred when it is essential to furtherreduce the concentration of the metal component in the resincomposition.

As homogeneous metal-containing catalysts there may be mentionedplatinum-divinyltetramethyldisiloxane, platinum-cyclicdivinylmethylsiloxane, platinic chloride, dichloroplatinum,tris(dibenzylideneacetone)diplatinum,bis(ethylene)tetrachlorodiplatinum, cyclooctadienedichloroplatinum,bis(cyclooctadiene)platinum, cyclooctadienedimethylplatinum,bis(triphenylphosphine)dichloroplatinum,tetrakis(triphenylphosphine)platinum and the like, or the compoundsmentioned in Comprehensive Handbook on Hydrosilylation, Pergamon Press(1992), ed. by B. Marciniec.

As heterogeneous metal-containing catalysts there may be mentionedsimple metal powders such as platinum powder, palladium powder or nickelpowder, simple supported metals such as platinum-carbon,platinum-alumina, platinum-silica, palladium-carbon, palladium-alumina,palladium-silica, rhodium-carbon, rhodium-alumina or rhodium-silica,Raney nickel, or the polymer-supported rhodium catalysts(polym-PPh₂.RhCl(PPh₃)₃, polym-PPh₂.RhCl₃, polym-CH₂Cl₂.RhCl(CO)(PPh₃)₂and the like) or polymer-supported platinum catalysts(polym-CH₂SH/H₂PtCl₆) described in Comprehensive Handbook onHydrosilylation, Pergamon Press (1992) edited by B. Marciniec or PolymerJournal, 34, 97-102(2002) (where “polym” means a main chain skeletonsuch as poly(styrene-co-divinylbenzene)), and silica gel-supportedplatinum catalysts with surface functional groups(Silica-(CH₂)₃—SH/H₂PtCl₆). These catalysts may be used alone or incombinations of two or more.

The amount of catalyst used is preferably in the range of 0.000001-5 asthe molar ratio of metal atoms with respect to the starting materialcompound present in the smaller molar amount among theB,B′,B″-trialkynylborazine compound or hydrosilane.

For production of a borazine-based resin represented by formula (2),there is used a polymerization solvent which maintains the fluidity ofthe system while facilitating removal of the metal-containing catalystafter polymerization. The polymerization solvent used may be any ofvarious solvents which do not react with the starting materials.Specifically, there may be mentioned aromatic hydrocarbon-based,saturated hydrocarbon-based, aliphatic ether-based and aromaticether-based solvents, and more specifically there may be mentionedtoluene, benzene, xylene, ethylbenzene, propylbenzene, hexylbenzene,hexane, tetrahydrofuran, ethyleneglycol dimethyl ether and diphenylether. These polymerization solvents may be used alone or incombinations of two or more.

The amount of polymerization solvent used is preferably 50-100,000 partsby weight of the polymerization solvent with respect to 100 parts byweight as the total of the B,B′,B″-trialkynylborazine or hydrosilane.

The charging molar ratio of the B,B′,B″-trialkynylborazine andhydrosilane for production of the borazine-based resin is preferably inthe range of 0.1-10 moles of the hydrosilane with respect to 1 mole ofthe B,B′,B″-trialkynylborazine, and more preferably in the range of0.2-5 moles of the hydrosilane with respect to 1 mole of theB,B′,B″-trialkynylborazine.

The reaction temperature and reaction time for production of theborazine-based resin are not particularly restricted so long as theconditions are such for polymerization of a B,B′,B″-trialkynylborazineand a hydrosilane to yield a borazine-based resin with the desiredmolecular weight. Specifically, cooling or heating may be carried outfor a reaction temperature in the range of −20° C. to 200° C., althoughthis will depend on the reactivity of the starting materials and thecatalyst activity. The reaction temperature is more preferably in therange of 0-150° C. and even more preferably in the range of 0-100° C.The reaction time is preferably from 1 minute to 10 days, morepreferably from 1 hour to 10 days and most preferably from 2 hours to 7days.

The polymerization reaction is preferably carried out in an inertatmosphere such as dry nitrogen or argon, but from the standpoint ofsimplifying the apparatus construction it may also be carried out inair.

By filtering the reaction solution to remove the metal-containingcatalyst after synthesis of the borazine-based resin, it is possible toobtain a filtrate containing the borazine-based resin. The filtrationmethod employed may be ordinary natural filtration, suction filtration,pressure filtration or the like. The filtering material used may befilter paper, filtering cloth or a resin film, while removal of thecatalyst by natural precipitation or centrifugation is also included as“filtration” according to the invention.

After completion of the polymerization reaction, particles which areinsoluble in the polymerization system and capable of adsorbing themetal component of the metal catalyst (metal scavengers) may be added tothe polymerization system (polymer solution), and the metalcomponent-adsorbed metal scavengers remaining in the polymer solutionsubsequently filtered out. Such treatment is particularly effective forreducing the metal content when employing a homogeneous metal-containingcatalyst.

The filtrate containing the borazine-based resin obtained in this mannermay then be concentrated under reduced pressure or heated toconcentration to remove the solvent, in order to obtain theborazine-based resin composition starting material as an insulating filmmaterial in the form of a solid polymer. The borazine-based resincomposition starting material can also be obtained by separation usingreprecipitation, a gel filtration column, GPC (gel permeationchromatography) or the like.

The borazine-based resin composition to be used as an insulating filmmaterial may be produced by the methods described above to obtain areaction solution filtrate resulting from the process of producing theborazine-based resin, the same filtrate combined with a solvent having ahigher boiling point than the polymerization solvent and having had thelow boiling point polymerization solvent removed, or a solution of thesolid borazine-based resin in a solvent.

As solvents or diluents capable of dissolving the borazine-based resincomposition there may be mentioned those which can dissolve but notreact with polymers having a borazine skeleton in the main chain or aside chain, i.e. borazine-based resins. Specifically, there may bementioned hydrocarbon solvents such as toluene, benzene, xylene,mesitylene, ethylbenzene, propylbenzene, hexylbenzene, tetralin,pentane, hexane, heptane, cyclohexane and dimethylcyclohexane, ethersolvents such as ethyleneglycol dimethyl ether, tetrahydrofuran,1,4-dioxane and diphenylether, ketone solvents such as acetone, methylethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclopentanoneand cyclohexanone, ester solvents such as ethyl acetate, butyl acetate,pentyl acetate and γ-butyrolactone, nitrogen-containing solvents such asN,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone and quinoline, halogen-based solvents such aschloroform, and dimethylsulfoxide.

These solvents or diluting solvents may be used alone or in combinationsof two or more. The amount of the solvent or diluting solvent used ispreferably such as to produce a borazine-based resin solid concentrationof 0.1-60 wt %.

The component including a borazine skeleton in its molecular structure,and therefore the insulating film of the invention which comprises it,preferably contains no metal components, and it is preferably formed ofa borazine-based resin composition with a metal impurity content of nogreater than 30 ppm and more preferably no greater than 10 ppm. A metalimpurity concentration exceeding 30 ppm will tend to result in leakcurrent due to metal components residing in the insulating film, or thespecific dielectric constant of the insulating film may excessivelyincrease, adversely affecting the device performance.

(First Borazine-Based Resin Production Process and Borazine-Based ResinComposition)

For the first borazine-based resin production process, theB,B′,B″-trialkynylborazine used in the first step (component x1;hereinafter referred to a simply as “x1”) is preferably a compoundrepresented by the following formula (3).

In formula (3) above, R¹ represents alkyl, aryl, aralkyl or hydrogen.The number of carbon atoms of the alkyl group is preferably 1-24 andmore preferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for group R¹ there may be mentioned alkyl groups such asmethyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such as phenyl,naphthyl and biphenyl, aralkyl groups such as benzyl and phenethyl, andhydrogen, among which methyl, ethyl, phenyl and hydrogen are especiallypreferred.

Also in formula (3), R² represents alkyl, aryl, aralkyl or hydrogen. Thenumber of carbon atoms of the alkyl group is preferably 1-24 and morepreferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for group R² there may be mentioned alkyl groups such asmethyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such as phenyl,naphthyl, biphenyl and anthracenyl, aralkyl groups such as benzyl,phenethyl and fluorenyl, and hydrogen, among which methyl, phenyl andhydrogen are especially preferred.

As more specific examples of B,B′,B″-trialkynylborazines represented byformula (3) there may be mentioned B,B′,B″-triethynylborazine,B,B′,B″-triethynyl-N,N′,N″-trimethylborazine,B,B′,B″-tri(1-propynyl)borazine, B,B′,B″-triphenylethynylborazine,B,B′,B″-triphenylethynyl-N,N′,N″-trimethylborazine,B,B′,B″-triethynyl-N,N′,N″-triphenylborazine,B,B′,B″-triphenylethynyl-N,N′,N″-triphenylborazine,B,B′,B″-ethynyl-N,N′,N″-tribenzylborazine andB,B′,B″-tris(1-propynyl)-N,N′,N″-trimethylborazine. However, there is nolimitation to these. Also, one of these B,B′,B″-trialkynylborazines maybe used alone, or two different B,B′,B″-trialkynylborazines may be usedin combination.

The hydrosilane used in the first step (component y1; hereinafterreferred to a simply as “y1”) is preferably a compound represented bythe following formula (4) or (5).

In formula (4), R³ and R⁴ represent identical or different monovalentgroups selected from among alkyl, aryl, aralkyl and hydrogen, amongwhich among which alkyl, aryl and hydrogen are preferred. In this case,the number of carbon atoms of the alkyl group is preferably 1-24 andmore preferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for groups R³ and R⁴ there may be mentioned alkyl groupssuch as methyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such asphenyl, naphthyl and biphenyl, aralkyl groups such as benzyl andphenethyl, and hydrogen, among which methyl, phenyl and hydrogen areespecially preferred.

Also in formula (4), R⁵ represents a substituted or unsubstitutedaromatic divalent group, an oxypoly(dimethylsiloxy) group or oxygen. Inthis case, the number of carbon atoms of the aromatic divalent group ispreferably 6-24 and more preferably 6-12. Aromatic divalent groupsinclude divalent aromatic hydrocarbon groups (arylene, etc.) and arylenegroups containing hetero atoms such as oxygen as connecting groups. Assubstituents to be bonded to the aromatic divalent group there may bementioned alkyl, aryl and aralkyl. More specifically, for group R⁵ theremay be mentioned arylene groups such as phenylene, naphthylene andbiphenylene, substituted arylene groups such as diphenylether, andoxygen, among which phenylene, diphenylether and oxygen are especiallypreferred.

In formula (5), R⁶ represents alkyl, aryl or hydrogen. In this case, thenumber of carbon atoms of the alkyl group is preferably 1-24 and morepreferably 1-12. The number of carbon atoms of the aryl group ispreferably 6-20 and more preferably 6-10. The number of carbon atoms ofthe aralkyl group is preferably 7-24 and more preferably 7-12. Morespecifically, for group R⁶ there may be mentioned alkyl groups such asmethyl, ethyl, isopropyl, t-butyl and octyl, aryl groups such as phenyl,naphthyl and biphenyl, and aralkyl groups such as benzyl and phenethyl.

Also in formula (5), n represents a positive integer of 2 or greater.The letters p and q in formula (2) above are in the followingrelationship with n: p+q+2=n. The preferred range for n is 2-10 and morepreferably 3-8. If n is excessively large (i.e. the ring is large), suchas greater than 10, the heat resistance and the mechanical properties ofthe insulating film described below will tend to be reduced to aninconvenient level.

The hydrosilanes (yl) represented by formula (4) or (5) includebis(monohydrosilane)s, bis(dihydrosilane)s, bis(trihydrosilane)s andpoly(hydrosilane)s. Specifically, there may be mentionedm-bis(dimethylsilyl)benzene, p-bis(dimethylsilyl)benzene,1,4-bis(dimethylsilyl)naphthalene, 1,5-bis(dimethylsilyl)naphthalene,m-bis(methylethylsilyl)benzene, m-bis(methylphenylsilyl)benzene,p-bis(methyloctylsilyl)benzene, 4,4′-bis(methylbenzylsilyl)biphenyl,4,4′-bis(methylphenethylsilyl)diphenylether, m-bis(methylsilyl)benzene,m-disilylbenzene, 1,1,3,3-tetramethyl-1,3-disiloxane,1,3,5,7-tetramethylcyclotetrasiloxane,1,3,5,7,9-pentamethylcyclopentasiloxane,1,3,5,7-tetraethylcyclotetrasiloxane, 1,3,5-triphenylcyclotrisiloxane,1,3,5,7-tetraphenylcyclotetrasiloxane and1,3,5,7-tetrabenzylcyclotetrasiloxane. However, there is no limitationto these.

Preferred among these are m-bis(dimethylsilyl)benzene,p-bis(dimethylsilyl)benzene, 1,1,3,3-tetramethyl-1,3-disiloxane and1,3,5,7-tetramethylcyclotetrasiloxane. Although one hydrosilane (y1) maybe used alone, two or more different hydrosilanes (y1) may also be usedin combination.

The solid catalyst (z1) used for the first step is preferably ametal-containing catalyst which promotes polymerization reaction of theB,B′,B″-trialkynylborazine (x1) and the hydrosilane (y1), whose metalcomponents do not elute in the reaction substrates (x1 and y1) or theoptionally added polymerization solvent described hereunder, and whichcan be removed by filtration after completion of the polymerization.

As specific examples for the solid catalyst (z1) there may be mentionedsimple metal powders such as platinum powder, palladium powder or nickelpowder; catalysts comprising a catalyst supported on a carbon-basedcarrier, such as platinum-carbon, palladium-carbon or rhodium-carbon;and catalysts comprising a catalyst supported on a compound-basedcarrier (non-carbon-based carrier). As catalysts comprising a catalystsupported on a compound-based carrier there may be mentioned metaloxide-supported catalysts such as platinum-alumina, platinum-silica,palladium-alumina, palladium-silica, rhodium-alumina and rhodium-silica;synthetic catalysts such as Raney nickel; the polymer-supported rhodiumcatalysts (polym-PPh₂.RhCl(PPh₃)₃, polym-PPh₂ RhCl₃,polym-CH₂Cl₂.RhCl(CO)(PPh₃)₂ and the like) or polymer-supported platinumcatalysts (polym-CH₂SH/H₂PtCl₆) described in Comprehensive Handbook onHydrosilylation, Pergamon Press (1992) edited by B. Marciniec or PolymerJournal, 34, 97-102(2002) (where “polym” means a main chain skeletonsuch as poly(styrene-co-divinylbenzene)); and silica gel-supportedplatinum catalysts with surface functional groups(Silica-(CH₂)₃—SH/H₂PtCl₆). These catalysts may be used alone or incombinations of two or more.

The solid catalyst (z1) is preferably a supported catalyst comprising acatalyst supported on a simple metal powder or compound-based carrier,and most preferably it is a supported catalyst comprising a catalystsupported on a compound-based carrier. Since the particle sizes of suchcatalysts can be easily controlled, it is possible to create large-sizedparticles relatively easily, and using a catalyst of such a size willfacilitate filtration of the catalyst from the reaction system. This isalso particularly effective for inhibiting leak current when theborazine-based resin is used as an insulating film. On the other hand,since a catalyst which comprises a catalyst supported on a carbon-basedcarrier is present in the form of fine powder, the precipitation rate inthe reaction system is slow and it is not always easy to remove thecatalyst to a satisfactory degree. Moreover, since the catalyst containsconductive carbon, leak current may be generated in the insulating filmwhen residual trace amounts of the catalyst are present.

When polymerization reaction between the B,B′,B″-trialkynylborazine (x1)and the hydrosilane (y1) is carried out in the first step, apolymerization solvent (component s1; hereinafter referred to simply as“s1”) may be added to maintain the fluidity of the system duringpolymerization and facilitate removal of the solid catalyst (z1) afterpolymerization. The polymerization solvent (s1) used may be any solventwhich does not react with the starting materials (x1, y1), dissolve thesolid catalyst (z1) or elute the metal components. As such solventsthere may be mentioned aromatic hydrocarbon-based, saturatedhydrocarbon-based, aliphatic ether-based and aromatic ether-basedsolvents, and more specifically there may be mentioned toluene, benzene,xylene, ethylbenzene, propylbenzene, hexylbenzene, hexane,tetrahydrofuran, ethyleneglycol dimethyl ether and diphenyl ether. Thesepolymerization solvents may be used alone or in combinations of two ormore.

The charging molar ratio of the B,B′,B″-trialkynylborazine (x) andhydrosilane (y) in the first step is preferably in the range of 0.1-10moles of the bis(hydrosilane) with respect to 1 mole of theB,B′,B″-trialkynylborazine, and more preferably in the range of 0.2-5moles of the bis(hydrosilane) with respect to 1 mole of theB,B′,B″-trialkynylborazine.

The amount of the solid catalyst (z) used is preferably in the range of0.000001-5 as the molar ratio of metal atoms with respect to thestarting material compound present in the smaller molar amount among theB,B′,B″-trialkynylborazine compound or hydrosilane.

The amount of polymerization solvent (s1) used in the first step ispreferably 50-100,000 parts by weight of the polymerization solvent (s1)with respect to 100 parts by weight as the total of theB,B′,B″-trialkynylborazine or hydrosilane.

The reaction temperature and reaction time for the first step are notparticularly restricted so long as the conditions are such forpolymerization of the B,B′,B″-trialkynylborazine and hydrosilane toyield a borazine-based resin with the desired molecular weight.Specifically, cooling or heating may be carried out for a reactiontemperature in the range of −20° C. to 200° C., although this willdepend on the reactivity of the starting materials and the catalystactivity. The reaction temperature is more preferably in the range of0-150° C. and even more preferably in the range of 0-100° C. Thereaction time is preferably from 1 minute to 10 days, more preferablyfrom 1 hour to 10 days and most preferably from 2 hours to 7 days.

The first step is preferably carried out in an inert atmosphere such asdry nitrogen or argon, but from the standpoint of simplifying theapparatus construction it may also be carried out in air.

After completion of the first step, the solid catalyst (z1) is thenremoved in the second step. The removal is preferably accomplished byfiltration of the reaction solution obtained in the first step. Thefiltration method employed may be ordinary natural filtration, suctionfiltration, pressure filtration or the like. The filtering material usedmay be filter paper, filtering cloth or a resin film, while removal ofthe catalyst by natural precipitation or centrifugation is also includedin the concept of “filtration”. Removal of the solid catalyst (z1) inthis manner will yield a filtrate containing the borazine-based resin(organic silicon/borazine-based polymer) having a reduced metal impuritycontent.

After completion of the second step, the obtained filtrate may then beconcentrated under reduced pressure or heated to concentration to removethe polymerization solvent (z1), in order to obtain the borazine-basedresin in the form of a solid polymer. The borazine-based resin startingmaterial can also be obtained by separation using reprecipitation, a gelfiltration column, GPC (gel permeation chromatography) or the like. Thefiltrate obtained in the second step may be directly used as theborazine-based resin composition (hereinafter, “C1”).

The borazine-based resin composition (C1) may be produced by uniformlymixing the borazine-based resin obtained by the borazine-based resinproduction process described above with a solvent as describedhereunder. Specifically, the filtrate obtained from the second step maybe used directly as the borazine-based resin composition (C1), or asolvent having a higher boiling point than the polymerization solventmay be added to the filtrate obtained from the second step and then thelow boiling point polymerization solvent removed. In the latter case,the borazine-based resin composition (C1) will be a mixture of the highboiling point solvent and the borazine-based resin. The borazine-basedresin composition (C1) may also be produced by dissolving a solidborazine polymer produced in the manner described above in the solventdescribed hereunder, after the second step.

As solvents capable of dissolving the borazine-based resin there may bementioned those which can dissolve but not react with the borazine-basedresin. As such solvents there may be mentioned hydrocarbon solvents suchas toluene, benzene, xylene, mesitylene, ethylbenzene, propylbenzene,hexylbenzene, tetralin, pentane, hexane, heptane, cyclohexane anddimethylcyclohexane, ether solvents such as ethyleneglycol dimethylether, tetrahydrofuran, 1,4-dioxane and diphenylether, ketone solventssuch as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutylketone, cyclopentanone and cyclohexanone, ester solvents such as ethylacetate, butyl acetate, pentyl acetate and y-butyrolactone,nitrogen-containing solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone and quinoline, halogen-based solvents such aschloroform, and dimethylsulfoxide.

These solvents or diluting solvents may be used alone or in combinationsof two or more. The amount of the solvent used is preferably such as toproduce a borazine-based resin solid concentration of 0.5-80 wt %,preferably 1-70 wt % and more preferably 2-60 wt %. If the solidconcentration is less than 0.5 wt %, the thickness of the film obtainedby a single coating onto the substrate will be small, and thereliability of the film, including its strength and heat resistance, aswell as its insulating property when dried as an insulating film, willbe reduced. On the other hand, if the solid concentration is greaterthan 80 wt %, the viscosity of the borazine-based resin composition (C1)will be excessively increased, tending to hamper efforts to form auniform thin film.

The borazine-based resin composition (C1) with such a construction hasan adequately minimized content of metal components from the solidcatalyst (z1) and of impurities such as halogens. The metal impuritycontent of the borazine-based resin composition (C1) is preferably nogreater than 30 ppm, more preferably no greater than 10 ppm and evenmore preferably no greater than 5 ppm, from the viewpoint of notadversely affecting the production apparatus for the insulating film,and not creating leak current when the insulating film is used as aninterlayer insulating film, or not impairing the characteristics of theinsulating film, such as the dielectric constant.

Incidentally, another possible method for reducing the impurityconcentration is a method of diluting the borazine-based resincomposition (C1) with a solvent having a very low impurityconcentration. However, while this method can reduce damage to theproduction apparatus for the insulating film, simultaneous reduction inthe solid concentration of the borazine-based resin composition (C1) mayalso result, such that no substantial reduction is achieved in theproportion of the impurity concentration with respect to the solidconcentration.

The insulating film A may also be formed from a borazine-based resincomposition comprising a borazine-based resin obtained by the firstborazine-based resin production process.

(Second Borazine-Based Resin Production Process and Borazine-Based ResinComposition)

In the second borazine-based resin production process, theborazine-based resin having a repeating unit represented by formula (2)above is produced by polymerizing the B,B′,B″-trialkynylborazine(component x2, hereinafter referred to simply as “x2”) and thehydrosilane (component y2; hereinafter referred to simply as “y2”) in apolymerization solvent (component s2; hereinafter referred to simply as“s2”) in the presence of a metal catalyst (component z2; hereinafterreferred to simply as “z2”) (first step), subsequently adding particleswhich are insoluble in the polymerization system and are capable ofadsorbing the metal component of the metal catalyst (metal scavengers)(component w; hereinafter referred to simply as “w”) (second step), andthen filtering out the metal scavengers onto which the metal componenthas been adsorbed (third step).

The B,B′,B″-trialkynylborazine (x2) and hydrosilane (y2) used in thesecond borazine-based resin production process are the same as x1 and y2described above. Also, the definitions and preferred examples for R¹ andR² in the B,B′,B″-trialkynylborazine and the specific examples ofB,B′,B″-trialkynylborazines are also the same, and the definitions andpreferred examples for R³ and R⁴ in the hydrosilane and the specificexamples of hydrosilanes are also the same. In the second borazine-basedresin production process as well, one or two or more differentB,B′,B″-trialkynylborazines may be used, and one or two or moredifferent hydrosilanes may be used.

The solid catalyst (z2) used for the second borazine-based resinproduction process may be one ordinarily used for hydrosilylation ofacetylenes or olefins. As specific examples for the solid catalyst (z2)there may be mentioned platinum-divinyltetramethyldisiloxane,platinum-cyclic divinylmethylsiloxane, platinic chloride,dichloroplatinum, tris(dibenzylideneacetone)diplatinum,bis(ethylene)tetrachlorodiplatinum, cyclooctadienedichloroplatinum,bis(cyclooctadiene)platinum, cyclooctadienedimethylplatinum,bis(triphenylphosphine)dichloroplatinum,tetrakis(triphenylphosphine)platinum and the like, or the compoundsmentioned in Comprehensive Handbook on Hydrosilylation, Pergamon Press(1992), ed. by B. Marciniec.

As additional specific examples for the metal catalyst (z2) there may bementioned simple metal powders such as platinum powder, palladium powderor nickel powder, simple supported metals such as platinum-carbon,platinum-alumina, platinum-silica, palladium-carbon, palladium-alumina,palladium-silica, rhodium-carbon, rhodium-alumina or rhodium-silica,Raney nickel, or the polymer-supported rhodium catalysts(polym-PPh₂.RhCl(PPh₃)₃, polym-PPh₂.RhCl₃, polym-CH₂Cl₂.RhCl(CO)(PPh₃)₂and the like) or polymer-supported platinum catalysts(polym-CH₂SH/H₂PtCl₆) described in Comprehensive Handbook onHydrosilylation, Pergamon Press (1992) edited by B. Marciniec or PolymerJournal, 34, 97-102(2002) (where “polym” means a main chain skeletonsuch as poly(styrene-co-divinylbenzene)), and silica gel-supportedplatinum catalysts with surface functional groups(Silica-(CH₂)₃—SH/H₂PtCl₆).

These metal catalysts (z2) may be used alone or in combinations of twoor more.

For production of a borazine-based resin represented by formula (2),there is used a polymerization solvent (s2) which maintains the fluidityof the system while facilitating removal of the metal scavenger (w)having the metal catalyst (z2)-derived metal component adhering theretoafter the polymerization. The polymerization solvent (s2) used may beany of various solvents which do not react with the starting materials.Specifically, there may be used the same ones as for the polymerizationsolvent (s1) described above, with the same preferred examples. One typeof polymerization solvent (s2) may be used alone, or two or more typesmay be used in combination.

The charging molar ratio of the B,B′,B″-trialkynylborazine (x2) andhydrosilane (y2) for production of the borazine-based resin representedby formula (2) is preferably in the range of 0.1-10 moles of thehydrosilane with respect to 1 mole of the B,B′,B″-trialkynylborazine,and more preferably in the range of 0.2-5 moles of the hydrosilane withrespect to 1 mole of the B,B′,B″-trialkynylborazine.

The amount of the metal catalyst (z2) used for production of theborazine-based resin represented by formula (2) is preferably in therange of 0.000001-5 as the molar ratio of metal atoms with respect tothe starting material compound present in the smaller molar amount amongthe B,B′,B″-trialkynylborazine compound or hydrosilane.

The amount of the polymerization solvent (s2) used for production of theborazine-based resin represented by formula (2) is preferably 50-100,000parts by weight of the polymerization solvent (s2) with respect to 100parts by weight as the total of the B,B′,B″-trialkynylborazine orhydrosilane.

The reaction temperature and reaction time for production of theborazine-based resin represented by formula (2) are not particularlyrestricted so long as the conditions are such for polymerization of aB,B′,B″-trialkynylborazine and a hydrosilane to yield a borazine-basedresin with the desired molecular weight. Specifically, cooling orheating may be carried out for a reaction temperature in the range of−20° C. to 200° C., although this will depend on the reactivity of thestarting materials and the catalyst activity. The reaction temperatureis more preferably in the range of 0-150° C. and even more preferably inthe range of 0-100° C. The reaction time is preferably from 1 minute to10 days, more preferably from 1 hour to 10 days and most preferably from2 hours to 7 days.

The polymerization reaction is preferably carried out in an inertatmosphere such as dry nitrogen or argon, but from the standpoint ofsimplifying the apparatus construction it may also be carried out inair.

After synthesis of the borazine-based resin, particles which areinsoluble in the polymerization system and capable of adsorbing themetal component of the metal catalyst (metal scavengers (w)) may beadded to the polymerization system (polymer solution), and the metalcomponent-adsorbed metal scavengers remaining in the polymer solutionsubsequently filtered out, for removal of the metal component of themetal catalyst (z2).

The metal scavengers (w) are particles which are capable of adsorbing(coordinating with) the metal component in the polymerization system andseparating it out of the polymerization system. Specifically, there maybe mentioned the following types of surface-modified particles which areused in “combinatorial chemistry”.

Here, ◯ represents styrene-divinylbenzene copolymer,polyethyleneglycol-polystyrene graft copolymer or silica gel. Irepresents an integer of 1 or greater.

Examples of other metal scavengers (w) include anionic exchange resins,silica gel particles, alumina particles, celite, active carbon powderand the like.

Although the amount of the metal scavengers (w) used will differdepending on the amount of the metal catalyst (z2) used for thepolymerization and/or the ability of the metal scavengers (w) to adsorb(coordinate with) the metal, in most cases the metal scavengers (w) arepreferably used at 0.01-100 parts by weight with respect to 100 parts byweight as the total of the reaction solution (x2+y2+z2+s2).

Also, by adding the metal scavengers (w) to the polymerization systemand stirring the solution, the metal scavengers will efficiently adsorb(coordinate with) the metal (second step). The time (contact time) foradsorption of the metal of the metal catalyst (z2) to the metalscavengers (w) will also differ depending on the amount of the metalcatalyst (z2) used and/or the ability of the metal scavengers (w) toadsorb (coordinate with) the metal, but in most cases it will be fromabout 10 minutes to 24 hours.

Next, the reaction solution is filtered to remove the metal scavengers(w) onto which the metal component has adsorbed, in order to obtain afiltrate containing the borazine-based resin with a reduced metalimpurity content (third step). The filtration method employed may beordinary natural filtration, suction filtration, pressure filtration orthe like. The filtering material used may be filter paper, filteringcloth or a resin film, while removal of the metal component-adsorbedmetal scavengers (w) by natural precipitation or centrifugation is alsoincluded as “filtration” according to the invention.

The filtrate containing the borazine-based resin obtained in this manneris the borazine-based resin composition (component C2; hereinafterreferred to simply as “C2”). The filtrate may be subjected toconcentration under reduced pressure or heating to concentration forremoval of the solvent, to obtain the borazine-based resin composition(C2) starting material in the form of a solid polymer. Theborazine-based resin composition (C2) starting material can also beobtained by separation using reprecipitation, a gel filtration column,GPC (gel permeation chromatography) or the like.

The solvent of the borazine-based resin composition (C2) (component B;hereinafter referred to simply as “B”) is one which dissolves but doesnot react with the polymer having a borazine skeleton on the main chainor a side chain (borazine-based resin). Specifically, there may bementioned hydrocarbon-based solvents such as toluene, benzene, xylene,mesitylene, ethylbenzene, propylbenzene, hexylbenzene, tetralin,pentane, hexane, heptane, cyclohexane and dimethylcyclohexane,ether-based solvents such as ethylene glycol dimethyl ether,tetrahydrofuran, 1,4-dioxane and diphenylether, ketone-based solventssuch as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutylketone, cyclopentanone and cyclohexanone, ester-based solvents such asethyl acetate, butyl acetate, pentyl acetate and y-butyrolactone,nitrogen-containing solvents such as N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone,N-cyclohexyl-2-pyrrolidone and quinoline, halogen-based solvents such aschloroform, and dimethylsulfoxide.

Any of these solvents (B) may be used alone or in combinations of two ormore. The amount of the solvent (B) used is preferably such as toproduce a borazine-based resin solid concentration of 0.5-80 wt %,preferably 1-70 wt % and more preferably 2-60 wt %. If the solidconcentration is less than 0.5 wt %, the thickness of the film obtainedby a single coating onto the substrate will be small, and thereliability of the film, including its strength and heat resistance, aswell as its insulating property when dried as an insulating film, willtend to be reduced. On the other hand, if the solid concentration isgreater than 80 wt %, the viscosity of the borazine-based resincomposition (C2) will be excessively increased, tending to hamperefforts to form a uniform thin film.

The borazine-based resin composition (C2) is a mixture (substantiallyhomogeneous mixture) of a borazine-based resin and the solvent (B). Theborazine-based resin composition (C2) may be produced by variousmethods, such as by adding a solvent having a higher boiling point thanthe polymerization solvent to the filtrate after filtration of the metalcomponent-adsorbed metal scavengers (w) obtained from the process ofproducing the borazine-based resin and then removing the low boilingpoint polymerization solvent (and hence a mixture of the high boilingpoint solvent and the borazine-based resin), or by dissolving a solidborazine-based resin in the solvent.

The borazine-based resin composition (C2) with such a construction hasan adequately minimized content of metal components from the solidcatalyst (z2) and of impurities such as halogens. The impurity contentof the borazine-based resin composition (C2) is preferably no greaterthan 30 ppm, more preferably no greater than 10 ppm and even morepreferably no greater than 5 ppm, from the viewpoint of not adverselyaffecting the production apparatus for the insulating film, and notcreating leak current when the insulating film is used as an interlayerinsulating film and not impairing the characteristics of the insulatingfilm, such as the dielectric constant.

Incidentally, another possible method for reducing the impurityconcentration of the borazine-based resin composition (C2) is a methodof diluting the borazine-based resin composition (C2) with a solventhaving a very low impurity concentration. However, while this method canreduce damage to the production apparatus for the insulating film,simultaneous reduction in the solid concentration of the borazine-basedresin composition (C2) may also result, such that no substantialreduction is achieved in the proportion of the impurity concentrationwith respect to the solid concentration.

The insulating film A may also be formed from a borazine-based resincomposition comprising a borazine-based resin obtained by the secondborazine-based resin production process.

(Insulating Film A and Electronic Part A)

An example of a method of forming an insulating film A using theaforementioned borazine-based resin composition will now be described.First, a film is formed by coating the borazine-based resin compositionon a substrate such as a silicon wafer, metal sheet or ceramic board bya method such as dipping, spraying, screen printing or spin coating. Thesolvent is then removed by heat drying the coating in air or an inertgas such as nitrogen at 60-500° C. for a period of about 10 seconds to 2hours. This can yield an insulating film composed of a non-sticky thinfilm. The thickness of the insulating film is not particularlyrestricted, but from the standpoint of heat resistance it is preferably0.05-50 μm, more preferably 0.1-10 μm and most preferably 0.2-5 μm.

As examples of an electronic part A using an insulating film A formed inthe manner described above there may be mentioned semiconductorelements, liquid crystal elements and multilayer wiring boards havinginsulating films. The insulating film of the invention is preferablyused as a surface protective film, buffer coat film or insulating filmsuch as an interlayer insulating film for a semiconductor element, as asurface protective film or insulating film for a liquid crystal element,or as an interlayer insulating film for a multilayer wiring board.

Specifically, as semiconductor elements there may be mentioned discretesemiconductor elements such as diodes, transistors, capacitors, compoundsemiconductor elements, thermistors, varistors and thyristors, memoryelements such as DRAM (dynamic random access memory), SRAM (staticrandom access memory), EPROM (erasable-programmable read only memory),mask ROM (mask read only memory), EEPROM (electricalerasable-programmable read only memory) and flash memory, logic(circuit) elements such as microprocessors, DSP and ASIC, integratedcircuit elements such as compound semiconductors typified by MMIC(monolithic microwave integrated circuits), and photoelectric conversionelements, light emitting elements and semiconductor laser elementsincluding hybrid integrated circuits, light emitting diodes andcharge-coupled device. As multilayer wiring boards there may bementioned high-density wiring boards such as MCM.

(Composite Insulating Film and Electronic Part B)

The first insulating film comprising a siloxane resin in a compositeinsulating film of the invention is not particularly restricted so longas it contains a polymer with a siloxane skeleton, and preferably it isa cured siloxane resin composition comprising a siloxane resin obtainedby hydrolytic condensation of a compound represented by the followingformula (1).X¹ _(n)SiX² _(4-n)   (1)In this formula, X¹ represents an H atom, an F atom, a group containinga B atom, N atom, Al atom, P atom, Si atom, Ge atom or Ti atom, or anorganic group of 1 to 20 carbons, X² represents a hydrolyzable group,and n represents an integer of 0-2, with the proviso that when n is 2,each X¹ may be the same or different, and when n is 0-2, each X² may bethe same or different.

As hydrolyzable groups for X² there may be mentioned alkoxy, halogens,acetoxy, isocyanate, hydroxyl and the like. Alkoxy groups are preferredamong these from the standpoint of the liquid stability and film coatingproperty of the composition used to form the first insulating film.

As examples of compounds wherein the hydrolyzable group X² is an alkoxygroup (alkoxysilanes) there may be mentioned tetraalkoxysilanes such astetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane,tetra-iso-propoxysilane, tetra-n-butoxysilane, tetra-sec-butoxysilane,tetra-tert-butoxysilane and tetraphenoxysilane, trialkoxysilanes such astrimethoxysilane, triethoxysilane, tripropoxysilane,fluorotrimethoxysilane, fluorotriethoxysilane, methyltrimethoxysilane,methyltriethoxysilane, methyltri-n-propoxysilane, methyltri-iso-propoxysilane, methyltri-n-butoxysilane, methyltri-iso-butoxysilane,methyltri-tert-butoxysilane, methyltriphenoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, ethyltri-n-propoxysilane,ethyltri-iso-propoxysilane, ethyltri-n-butoxysilane,ethyltri-iso-butoxysilane, ethyltri-tert-butoxysilane,ethyltriphenoxysilane, n-propyltrimethoxysilane,n-propyltriethoxysilane, n-propyltri-n-propoxysilane,n-propyltri-iso-propoxysilane, n-propyltri-n-butoxysilane,n-propyltri-iso-butoxysilane, n-propyltri-tert-butoxysilane,n-propyltriphenoxysilane, iso-propyltrimethoxysilane,iso-propyltriethoxysilane, iso-propyltri-n-propoxysilane,iso-propyltri-iso-propoxysilane, iso-propyltri-n-butoxysilane,iso-propyltri-iso-butoxysilane, iso-propyltri-tert-butoxysilane,iso-propyltriphenoxysilane, n-butyltrimethoxysilane,n-butyltriethoxysilane, n-butyltri-n-propoxysilane,n-butyltri-iso-propoxysilane, n-butyltri-n-butoxysilane,n-butyltri-iso-butoxysilane, n-butyltri-tert-butoxysilane,n-butyltriphenoxysilane, sec-butyltrimethoxysilane,sec-butyltriethoxysilane, sec-butyltri-n-propoxysilane,sec-butyltri-iso-propoxysilane, sec-butyltri-n-butoxysilane,sec-butyltri-iso-butoxysilane, sec-butyltri-tert-butoxysilane,sec-butyltriphenoxysilane, t-butyltrimethoxysilane,t-butyltriethoxysilane, t-butyltri-n-propoxysilane,t-butyltri-iso-propoxysilane, t-butyltri-n-butoxysilane,t-butyltri-iso-butoxysilane, t-butyltri-tert-butoxysilane,t-butyltriphenoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane,phenyltri-n-propoxysilane, phenyltri-iso-propoxysilane,phenyltri-n-butoxysilane, phenyltri-iso-butoxysilane,phenyltri-tert-butoxysilane, phenyltriphenoxysilane,trifluoromethyltrimethoxysilane, pentafluoroethyltrimethoxysilane,3,3,3-trifluoropropyltrimethoxysilane and3,3,3-trifluoropropyltriethoxysilane, diorganodialkoxysilanes such asdimethyldimethoxysilane, dimethyldiethoxysilane,dimethyldi-n-propoxysilane, dimethyldi-iso-propoxysilane,dimethyldi-n-butoxysilane, dimethyldi-sec-butoxysilane,dimethyldi-tert-butoxysilane, dimethyldiphenoxysilane,diethyldimethoxysilane, diethyldiethoxysilane,diethyldi-n-propoxysilane, diethyldi-iso-propoxysilane,diethyldi-n-butoxysilane, diethyldi-sec-butoxysilane,diethyldi-tert-butoxysilane, diethyldiphenoxysilane,di-n-propyldimethoxysilane, di-n-propyldiethoxysilane,di-n-propyldi-n-propoxysilane, di-n-propyldi-iso-propoxysilane,di-n-propyldi-n-butoxysilane, di-n-propyldi-sec-butoxysilane,di-n-propyldi-tert-butoxysilane, di-n-propyldiphenoxysilane,di-iso-propyldimethoxysilane, di-iso-propyldiethoxysilane,di-iso-propyldi-n-propoxysilane, di-iso-propyldi-iso-propoxysilane,di-iso-propyldi-n-butoxysilane, di-iso-propyldi-sec-butoxysilane,di-iso-propyldi-tert-butoxysilane, di-iso-propyldiphenoxysilane,di-n-butyldimethoxysilane, di-n-butyldiethoxysilane,di-n-butyldi-n-propoxysilane, di-n-butyldi-iso-propoxysilane,di-n-butyldi-n-butoxysilane, di-n-butyldi-sec-butoxysilane,di-n-butyldi-tert-butoxysilane, di-n-butyldiphenoxysilane,di-sec-butyldimethoxysilane, di-sec-butyldiethoxysilane,di-sec-butyldi-n-propoxysilane, di-sec-butyldi-iso-propoxysilane,di-sec-butyldi-n-butoxysilane, di-sec-butyldi-sec-butoxysilane,di-sec-butyldi-tert-butoxysilane, di-sec-butyldiphenoxysilane,di-tert-butyldimethoxysilane, di-tert-butyldiethoxysilane,di-tert-butyldi-n-propoxysilane, di-tert-butyldi-iso-propoxysilane,di-tert-butyldi-n-butoxysilane, di-tert-butyldi-sec-butoxysilane,di-tert-butyldi-tert-butoxysilane, di-tert-butyldiphenoxysilane,diphenyldimethoxysilane, diphenyldiethoxysilane,diphenyldi-n-propoxysilane, diphenyldi-iso-propoxysilane,diphenyldi-n-butoxysilane, diphenyldi-sec-butoxysilane,diphenyldi-tert-butoxysilane, diphenyldiphenoxysilane,bis(3,3,3-trifluoropropyl)dimethoxysilane andmethyl(3,3,3-trifluoropropyl)dimethoxysilane.

In addition to the alkoxysilanes mentioned above, there may also bementioned as compounds represented by formula (1) halogenosilaneswherein the alkoxy group of the aforementioned alkoxysilane molecule isreplaced with a halogen, acetoxysilanes wherein the same alkoxy group isreplaced with an acetoxy group, isocyanatesilanes wherein the samealkoxy group is replaced with an isocyanate group, and silanols whereinthe same alkoxy group is replaced with a hydroxyl group. Any of thesecompounds represented by formula (1) may be used alone, or two or moredifferent ones may be used in combination.

The catalyst used to promote the hydrolytic condensation reaction forhydrolytic condensation of the compound represented by formula (1) maybe an acidic catalyst or a basic catalyst. As acidic catalysts there maybe mentioned organic acids such as formic acid, maleic acid, fumaricacid, acetic acid, propionic acid, butanoic acid, pentanoic acid,hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoicacid, oxalic acid, adipic acid, sebacic acid, butyric acid, oleic acid,stearic acid, linoleic acid, linolenic acid, salicylic acid, benzoicacid, p-aminobenzoic acid, p-toluenesulfonic acid, phthalic acid,sulfonic acid, tartaric acid and trifluoromethanesulfonic acid, as wellas hydrochloric acid, phosphoric acid, nitric acid, boric acid, sulfuricacid and hydrofluoric acid. Examples of basic catalysts include ammonia,organic amines and the like.

The catalyst used to promote the hydrolytic condensation reaction ispreferably used in a range of 0.0001-1 mole with respect to 1 mole ofthe compound represented by formula (1). If used in an amount of lessthan 0.0001 mole, the polymerization reaction will probably not proceedto a sufficient degree. It is preferably not used at greater than 1 molebecause this may tend to promote gelling.

The alcohol by-product of the hydrolytic condensation reaction may beremoved using an evaporator or the like as necessary. Also, the amountof water in the hydrolytic condensation reaction system may be set asappropriate, and is preferably in the range of 0.5-20 moles with respectto 1 mole of the compound represented by formula (1). If the amount ofwater is outside of the range of 0.5-20 moles, the film forming propertymay be impaired and the storage stability may be reduced.

From the standpoint of solubility in the solvent, mechanical propertiesand moldability, the siloxane resin obtained by hydrolytic condensationof the compound represented by formula (1) preferably has a weightaverage molecular weight of 500-20,000 and more preferably 1000-10,000as the value measured by gel permeation chromatography (GPC) based on astandard polystyrene calibration curve.

The siloxane resin composition used to form the first insulating filmwill usually contain a solvent as an essential component. As examples ofsuch solvents there may be mentioned alcohol-based solvents such asmethanol, ethanol, n-propanol, i-propanol, n-butanol, i-butanol,sec-butanol, t-butanol, n-pentanol, i-pentanol, 2-methylbutanol,sec-pentanol, t-pentanol, 3-methoxybutanol, n-hexanol, 2-methylpentanol,sec-hexanol, 2-ethylbutanol, sec-heptanol, n-octanol, 2-ethylhexanol,sec-octanol, n-nonyl alcohol, n-decanol, sec-undecyl alcohol,trimethylnonyl alcohol, sec-tetradecyl alcohol, sec-heptadecyl alcohol,phenol, cyclohexanol, methylcyclohexanol, benzyl alcohol, ethyleneglycol, 1,2-propylene glycol, 1,3-butylene glycol, diethylene glycol,dipropylene glycol, triethylene glycol and tripropylene glycol,ketone-based solvents such as acetone, methyl ethyl ketone,methyl-n-propyl ketone, methyl-n-butyl ketone, methyl-iso-butyl ketone,methyl-n-pentyl ketone, methyl-n-hexyl ketone, diethyl ketone,di-iso-butyl ketone, trimethylnonanone, cyclohexanone, cyclopentanone,methylcyclohexanone, 2,4-pentanedione, acetonylacetone, diacetonealcohol, acetophenone and γ-butyrolactone, ether-based solvents such asethyl ether, iso-propyl ether, n-butyl ether, n-hexyl ether,2-ethylhexyl ether, ethylene oxide, 1,2-propylene oxide, dioxolane,4-methyldioxolane, dioxane, dimethyldioxane, ethyleneglycol monomethylether, ethyleneglycol monoethyl ether, ethyleneglycol diethyl ether,ethyleneglycol mono-n-hexyl ether, ethyleneglycol monophenyl ether,ethyleneglycol mono-2-ethylbutyl ether, ethyleneglycol dibutyl ether,diethyleneglycol monoethyl ether, diethyleneglycol diethyl ether,diethyleneglycol diethyl ether, diethyleneglycol mono-n-butyl ether,diethyleneglycol di-n-butyl ether, diethyleneglycol mono-n-hexyl ether,ethoxy triglycol, tetraethyleneglycol di-n-butyl ether, propyleneglycolmonomethyl ether, propyleneglycol monoethyl ether, propyleneglycolmonopropyl ether, dipropyleneglycol monomethyl ether, dipropyleneglycolmonoethyl ether, tripropyleneglycol monomethyl ether, tetrahydrofuranand 2-methyltetrahydrofuran, ester-based solvents such as methylacetate, ethyl acetate, n-propyl acetate, i-propyl acetate, n-butylacetate, i-butyl acetate, sec-butyl acetate, n-pentyl acetate,sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl acetate,2-ethylbutyl acetate, 2-ethylhexyl acetate, benzyl acetate, cyclohexylacetate, methylcyclohexyl acetate, nonyl acetate, γ-butyrolactone,γ-valerolactone, methyl acetoacetate, ethyl acetoacetate, ethyleneglycolmonomethyl ether acetate, ethyleneglycol monoethyl ether acetate,diethyleneglycol monomethyl ether acetate, diethyleneglycol monoethylether acetate, diethyleneglycol mono-n-butyl ether acetate,propyleneglycol monomethyl ether acetate, propyleneglycol monoethylether acetate, propyleneglycol monopropyl ether acetate,dipropyleneglycol monomethyl ether acetate, dipropyleneglycol monoethylether acetate, glycol diacetate, methoxytriglycol acetate, ethylpropionate, n-butyl propionate, i-amyl propionate, diethyl oxalate,di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl lactate andn-amyl lactate, as well as acetonitrile, N,N-dimethylformamide,N,N-dimethylacetamide and N,N-dimethylsulfoxide, among which any onealone or two or more different ones in combination may be used.

The amount of solvent used in the siloxane resin composition ispreferably such as to produce a siloxane resin concentration of 3-25 wt%. If the amount of solvent used is too small such that the siloxaneresin concentration exceeds 25 wt %, the liquid stability and filmforming property will tend to be reduced to an inconvenient level. Onthe other hand, if the amount of solvent used is too large such that thesiloxane resin concentration is less than 3 wt %, it will tend to bedifficult to obtain a first insulating film having the desired filmthickness.

A pore-forming material may optionally be added to the siloxane resincomposition of the invention as necessary. As specific examples ofpore-forming materials there may be mentioned polymers including(meth)acrylic acid derivatives such as acrylic acid, 2-hydroxyethylacrylate, diethyleneglycol acrylate, 2-hydroxypropyl acrylate,dipropyleneglycol acrylate, methacrylic acid, 2-hydroxyethylmethacrylate, diethyleneglycol methacrylate, 2-hydroxypropylmethacrylate and dipropyleneglycol methacrylate, as well as vinylalcohol, allyl alcohol vinyl ether-based compounds, vinyl-basedcompounds with polyethylene oxide structures, vinyl-based compounds withpolypropylene oxide structures, vinylpyridine-based compounds,styrene-based compounds, alkyl ester/vinyl-based compounds,(meth)acrylate/acid-based compounds, propylene glycol-based compoundsand ethylene glycol-based compounds.

The method for forming a composite insulating film according to theinvention may be a method such as dipping, spraying, screen printing orspin coating, among which spin coating is preferred in most cases inconsideration of the film forming property and uniformity of filmthickness.

When a spin coating method is employed, the siloxane resin compositionis preferably spin coated onto a substrate such as silicon wafer, metalsheet or ceramic board at 500-5000 rpm and more preferably 1000-3000rpm. If the spin coating rotation rate is less than 500 rpm, the filmthickness uniformity will tend to be inferior, and if it is greater than5000 rpm, the film forming property will tend to be inferior.

The solvent is preferably removed by drying using a hot plate at 50-300°C. and more preferably 100-300° C. This will form a first insulatingfilm on the substrate. If the drying temperature is below 50° C., thesolvent drying will tend to be insufficient. If the drying temperatureis above 300° C., and the siloxane resin composition includes apore-forming material such as a thermal decomposing volatile compound,it will tend to thermally decompose and volatilize before the siloxaneskeleton forms, thereby making it impossible to achieve the desireddielectric property.

The borazine-based resin composition is preferably coated onto the firstinsulating film-formed substrate by spin coating at 500-5000 rpm andmore preferably 1000-3000 rpm, and the solvent is removed by dryingusing a hot plate or curing oven at 50-300° C. and more preferably100-300° C. This will form a second insulating film on the firstinsulating film.

Final curing is carried out in air or an inert gas such as nitrogen,preferably at 60-500° C. and preferably for a period of about 10 secondsto 2 hours, to obtain a composite insulating film according to theinvention. The apparatus used is preferably a quartz tube furnace, hotplate, rapid thermal annealing heater or lamp heating apparatus.

The film thickness of the bilayer structure composite insulating filmobtained in this manner is preferably 0.01-40 μm and more preferably0.1-2.0 ρm. A film thickness of greater than 40 μm may lead tostress-related cracking, while a thickness of less than 0.1 μm will tendto result in inferior interwiring leak characteristics when a wiringlayer is provided above and below the composite insulating film.

FIG. 1 is a schematic cross-sectional view showing an example of acomposite insulating film according to the invention. The compositeinsulating film shown in this drawing comprises a siloxaneresin-containing insulating film 102 formed on a silicon wafer 100having a metal wiring layer 101 provided on a silicon substrate layer(first insulating film), which is coated with a borazine-basedresin-containing insulating film 103 (second insulating film). Thecomposite insulating film may be easily formed by the spin coatingmethod described above.

As electronic parts B employing the composite insulating film of theinvention there may be mentioned parts with insulating films, such assemiconductor elements, liquid crystal elements and multilayer wiringboards. In a semiconductor element, the composite insulating film of theinvention is preferably used as a surface protective film, buffer coatfilm or insulating film such as an interlayer insulating film, in aliquid element it is preferably used as a surface protective film orinsulating film, and in a multilayer wiring board it is preferably usedas an interlayer insulating film. It may also be useful as a laminate(structure) wherein another upper film, such as a hard mask,anti-reflection (AR) film, reflection film, resist film or the likecovers the second insulating film which contains a borazine skeleton inthe molecular structure. Of particular utility is a laminated bodyformed with a hard mask, which is necessary for formation of a metalwiring pattern on the insulating film and which requires firm adhesion.

Specifically, as semiconductor elements there may be mentioned the sametypes of semiconductor elements mentioned for the electronic part A. Asmultilayer wiring boards there may be mentioned high-density wiringboards such as MCM.

(Insulating Film Employing Borazine-Based Resin, and Electronic Part C)

The aforementioned borazine-based resin composition (C1 or C2) may beused to form an insulating film of the invention by the followingmethod. Specifically, first a film is formed by coating theborazine-based resin composition (C1 or C2) on a substrate such as asilicon wafer, metal sheet or ceramic board by a method such as dipping,spraying, screen printing or spin coating. The solvent is then removedby heat drying the coating in air or an inert gas such as nitrogen at60-500° C. for a period of about 10 seconds to 2 hours. This can yieldan insulating film composed of a non-sticky thin film. The thickness ofthe insulating film is not particularly restricted, but from thestandpoint of heat resistance it is preferably 0.05-50 μm, morepreferably 0.1-10 μm and most preferably 0.2-5 μm.

As examples of an electronic part C using an insulating film formed inthe manner described above there may be mentioned semiconductorelements, liquid crystal elements and multilayer wiring boards havinginsulating films. The insulating film of the invention is preferablyused as a surface protective film, buffer coat film or insulating filmsuch as an interlayer insulating film for a semiconductor element, as asurface protective film or insulating film for a liquid crystal element,or as an interlayer insulating film for a multilayer wiring board.

Specifically, as semiconductor elements there may be mentioned the samesemiconductor elements mentioned above for electronic part A. Asmultilayer wiring boards there may be mentioned high-density wiringboards such as MCM.

(Preferred Embodiments of Electronic Parts A-C)

FIG. 2 is a schematic cross-sectional view showing a preferredembodiment of an electronic part A-C according to the invention. Thismemory capacitor cell 8 (electronic part) comprises an interlayerinsulating film (composite insulating film) having a bilayer structurecomposed of an insulating layer 5 (first insulating film) and aninsulating layer 7 (second insulating film) formed by a spin coatingmethod, formed between a counter electrode 8C provided above and a gateelectrode 3 (functioning as a word line) below which is situated on asilicon wafer 1 (substrate) provided with diffusion regions 1A,1B, via agate insulating film 2B composed of an oxidation film.

Side wall oxidation films 4A,4B are formed on the side walls of the gateelectrode 3, while a field oxidation film 2A is formed on the diffusionregion 1B beside the gate electrode, for separation of the element. Acontact hole 5A is formed in the insulating layer 5 for embedding of anelectrode 6 which functions as a bit line near the gate electrode 3. Aflattened insulating layer 7 covers the flattened insulating layer 5,and a storage electrode 8A is embedded in the contact hole 7A formedthrough both layers. Also, a counter electrode 8C is provided on thestorage electrode 8A via a capacitor insulating film 8B composed of ahigh dielectric body.

The insulating layer 5 and insulating layer 7 may have either the samecomposition or different compositions. The insulating layer 5 and/orinsulating layer 7 may be insulating films A, and the borazine-basedresin composition comprising a borazine-based resin obtained by thefirst or second borazine-based resin production process may be used toform the insulating films by the forming method described above.Alternatively, the insulating layer 5 may be the first insulating filmand the insulating layer 7 may be the second insulating film, as acomposite insulating film.

An electronic part such as a memory capacitor cell 8 having theinsulating film A formed thereon exhibits an adequately reduced specificdielectric constant of the insulating film compared to the prior art, sothat the wiring delay time for signal propagation can be satisfactorilyshortened and leak current can be effectively prevented. As a result,higher performance of the element can be realized and higher reliabilitycan be achieved. Such characteristics can also be obtained when theinsulating film is formed using a borazine-based resin compositioncomprising a borazine-based resin obtained by the first or secondborazine-based resin production process.

On the other hand, in an electronic part such as a memory capacitor cell8 having first and second insulating films formed thereon, theinterlayer insulating films consist of an insulating layer 5 comprisinga siloxane resin and an insulating layer 7 comprising a borazine-basedresin, and therefore satisfactorily reduced specific dielectric constantcan be achieved. It is thereby possible to sufficiently shorten thewiring delay time for signal propagation. In addition, since the filmstrength of the composite insulating film is adequately increased andsatisfactorily strong bonding is formed between the insulating layers5,7 and between the insulating layer 7 and the counter electrode 8C,interlayer peeling is prevented during the polishing steps such as CMPin the production processes for electronic products such as memorycapacitor cells 8, thereby helping to prevent reduced product yields andimprove device reliability.

EXAMPLES

The present invention will now be explained in greater detail byexamples, with the understanding that the invention is not limited tothese examples.

Production Example 1-1

(Production of Borazine-Based Resin Composition 1-1)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol ofp-bis(dimethylsilyl)benzene in 4 ml of ethylbenzene, 5% platinum-alumina(0.1 mmol as platinum) was added and the mixture was stirred for 7 daysunder nitrogen at 50° C. A portion of the reaction solution was sampledand analyzed by gas chromatography (GC), confirming disappearance of thepeaks for the B,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers. The molecular weight of theproduct as determined by GPC analysis (based on standard polystyrene)was Mn=2500 (Mw/Mn=2.0). The reaction solution containing theplatinum-alumina catalyst was filtered with a disposable membrane filterunit by ADVANTEC to obtain a borazine-based resin composition 1-1.

Production Example 1-2

(Production of Borazine-Based Resin Composition 1-2)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol of1,3,5,7-tetramethylcyclotetrasiloxane in 4 ml of ethylbenzene, 5%platinum-alumina (0.1 mmol as platinum) was added and the mixture wasstirred for 7 days under nitrogen at 50° C. A portion of the reactionsolution was sampled and analyzed by gas chromatography (GC), confirmingdisappearance of the peak for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine monomer. The molecularweight of the product as determined by GPC analysis (based on standardpolystyrene) was Mn=3000 (Mw/Mn=2.2). The reaction solution containingthe platinum-alumina catalyst was filtered with a disposable membranefilter unit by ADVANTEC to obtain a borazine-based resin composition1-2.

Production Example 1-3

(Production of Borazine-Based Resin Composition 1-3)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol ofp-bis(dimethylsilyl)benzene in 4 ml of ethylbenzene, thepolymer-supported platinum catalyst described in Polymer Journal, 34,97-102(2002) (Polym-CH₂SH/H₂PtCl₆) (0.01 mmol as platinum) was added andthe mixture was stirred for 5 days under nitrogen at 50° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming disappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers. The molecular weight of theproduct as determined by GPC analysis (based on standard polystyrene)was Mn=3800 (Mw/Mn=2.5). The reaction solution containing thepolymer-supported platinum catalyst was filtered with a disposablemembrane filter unit by ADVANTEC to obtain a borazine-based resincomposition 1-3.

Production Example 1-4

(Production of Borazine-Based Resin Composition 1-4)

After dissolving 3.6 g (15 mmol) ofB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and 3.6 g (15 mmol)of 1,3,5,7-tetramethylcyclotetrasiloxane in 150 ml of mesitylene, 30 μlof a solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 1 day undernitrogen at 40° C. After adding an additional 30 μl of a solution ofplatinum-divinyltetramethyldisiloxane in xylene (2% platinum content),the mixture was further stirred for 1 day under nitrogen at 40° C. Next,0.36 g (1.5 mmol) of 1,3,5,7-tetramethylcyclotetrasiloxane was added andstirring was continued for 1 day under nitrogen at 40° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming disappearance of the peaks for the B,B′,B-tris(1′-propynyl)-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane monomers. The molecular weight ofthe product as determined by GPC analysis (based on standardpolystyrene) was Mn=11,000 (Mw/Mn=29).

After then adding 1.0 g of metal scavengers of formula (9)(3-mercaptopropyl-functionalized silica gel, product of Aldrich) to thereaction solution, it was stirred at room temperature for 2 hours. Theplatinum-adsorbed metal scavengers were filtered out on a PTFE membranefilter by ADVANTEC to obtain a borazine-based resin composition 1-4according to the invention.

Production Example 1-5

(Production of Platinum-Containing Borazine-Based Resin Composition 1-5)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol ofp-bis(dimethylsilyl)benzene in 8 ml of ethylbenzene, 15 μl of a solutionof the homogeneous metal catalyst platinum-divinyltetramethyldisiloxanein xylene (2% platinum content) was added and the mixture was stirredfor 3 days under nitrogen at room temperature. A portion of the reactionsolution was sampled and analyzed by gas chromatography (GC), confirmingdisappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers. The molecular weight of theproduct as determined by GPC analysis (based on standard polystyrene)was Mn=4300 (Mw/Mn=2.5). The reaction solution was used as theborazine-based resin composition 5.

Example 1-1

(Production of Insulating Film 1-1)

The borazine-based resin composition 1-1 obtained in Production Example1-1 was filtered through a filter and the filtrate was added dropwiseonto a low resistivity silicon wafer (substrate; resistivity <10 Ωcm)for spin coating. The silicon wafer was then heated for 1 hour on a hotplate at 200° C. in a nitrogen atmosphere, and then baked at 300° C. for30 minutes and at 400° C. for 30 minutes, to obtain an insulating film1-1 of the invention.

Example 1-2

(Production of Insulating Film 1-2)

An insulating film 1-2 of the invention was obtained in the same manneras Example 1-1, except that the borazine-based resin composition 1-2obtained in Production Example 1-2 was used instead of theborazine-based resin composition 1-1.

Example 1-3

(Production of Insulating Film 1-3)

An insulating film 1-3 of the invention was obtained in the same manneras Example 1-1, except that the borazine-based resin composition 1-3obtained in Production Example 1-3 was used instead of theborazine-based resin composition 1-1.

Example 1-4

(Production of Insulating Film 1-4)

An insulating film 1-4 of the invention was obtained in the same manneras Example 1-1, except that the borazine-based resin composition 1-4obtained in Production Example 1-4 was used instead of theborazine-based resin composition 1-1.

Comparative Example 1-1

(Production of Insulating Film 1-5)

An insulating film 1-5 of the invention was obtained in the same manneras Example 1-1, except that the borazine-based resin composition 1-5obtained in Production Example 1-5 was used instead of theborazine-based resin composition 1-1.

<Measurement of Metal Content>

The metal content of the borazine-based resin composition was measuredby atomic absorption spectrometry using an AA-6650G by ShimadzuLaboratories. The platinum concentrations of the borazine-based resincompositions 1-1 to 1-5 are shown in Table 1. TABLE 1 PlatinumBorazine-based resin composition concentration (ppm) 1-1 (ProductionExample 1-1) 2 1-2 (Production Example 1-2) 2 1-3 (Production Example1-3) 6 1-4 (Production Example 1-4) 2 1-5 (Production Example 1-5) 50<Measurement of Specific Dielectric Constant>

The specific dielectric constant was measured for each insulating filmobtained in the examples and comparative example. The “specificdielectric constant” of an insulating film according to the invention isthe value measured in an atmosphere of 23° C.±2° C., 40±10% humidity,and it is determined by measuring the charge capacity between Al metaland an N-type low resistivity wafer (Si wafer).

Specifically, after forming the insulating film of each of the examplesand comparative example, a vacuum vapor deposition apparatus was usedfor vacuum vapor deposition of Al metal with a diameter of 2 mm onto theinsulating film to a thickness of about 0.1 μm. This formed a structurewherein the insulating film was situated between Al metal and a lowresistivity wafer. The charge capacity of this structure was thenmeasured at a use frequency of 1 MHz, using an apparatus comprising anLF impedance analyzer (HP4192A by Yokogawa Denki) connected to adielectric test fixture (HP16451B by Yokogawa Denki).

The measured value of the charge capacity was substituted into thefollowing formula:Specific dielectric constant of insulating film=3.597×10⁻²×chargecapacity (pF)×insulating film thickness (μm),to calculate the specific dielectric constant of the insulating film.The thickness of the insulating film was the value measured with anL116B ellipsometer by Gartner Japan.<Measurement of Leak Current>

After measuring the specific dielectric constant of each wafer, the leakcurrent was measured using a leak current measuring device.

<Measurement of Young's Modulus)

The Young's modulus of each insulating film was measured using a DCMnanoindenter by MTS Co., as an index of the film strength.

The results of measuring the specific dielectric constants, leakcurrents and Young's moduli of the insulating films 1-1 to 1-5 are shownin Table 2. TABLE 2 Specific dielectric Leak current Young's Insulatingfilm constant (−) (A/cm²) modulus (GPa) 1-1 2.1 1 × 10⁻⁹ 8 (Example 1-1)1-2 2.1 1 × 10⁻⁹ 9 (Example 1-2) 1-3 2.2 2 × 10⁻⁹ 9 (Example 1-3) 1-42.3 1 × 10⁻⁹ 7 (Example 1-4) 1-5 2.7 1 × 10⁻⁷ 9 (Comp. Ex. 1-1)

Example 2-1

(Production of Siloxane Resin Composition 2-1)

To a solution of 132.3 g of tetraethoxysilane and 65.1 g ofmethyltriethoxysilane in 335.94 g of propyleneglycol monopropyl ether(PGP) there was added a solution of 0.92 g of 70% nitric acid in 65.8 gof water, dropwise over a period of 30 minutes while stirring. Aftercompletion of the dropwise addition, reaction was conducted for 5 hoursto obtain a polysiloxane solution. Next, 22.9 g of a methyl methacrylatepolymer solution was added and the produced ethanol was distilled offunder reduced pressure in a warm bath to obtain 630 g of a siloxaneresin composition 2-1.

(Production of Borazine-Based Resin Composition 2-1)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol ofp-bis(dimethylsilyl)benzene in 4 ml of ethylbenzene, 5% platinum-alumina(0.1 mmol as platinum) was added and the mixture was stirred for 7 daysunder nitrogen at room temperature. A portion of the reaction solutionwas sampled and analyzed by gas chromatography (GC), confirmingdisappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers. The molecular weight of theproduct as determined by GPC analysis (based on standard polystyrene)was Mn=2500 (Mw/Mn=2.0). The reaction solution containing theplatinum-alumina catalyst was filtered with a disposable membrane filterunit by ADVANTEC to obtain a borazine-based resin composition 2-1.

(Formation of Composite Insulating Film 2-1)

First, a siloxane resin composition was passed through a filter and spincoated onto a low resistivity silicon wafer (resistivity <10 Ωcm) at2000 rpm/30 sec. The solvent was then removed at 150° C./1 min+250° C./1min to form a first insulating film. This was followed by spin coatingof a borazine-based resin composition at 1000 rpm/30 sec. The solventwas then removed at 200° C./10 min to form a second insulating film. Thewafer was then subjected to 400° C./30 min in a quartz tube furnace withthe O₂ concentration controlled to about 100 ppm for final curing ofboth insulating films, to obtain a composite insulating film 2-1 of theinvention.

Example 2-2

(Production of Siloxane Resin Composition 2-2)

To a solution of 132.3 g of tetraethoxysilane and 65.1 g ofmethyltriethoxysilane in 335.94 g of propyleneglycol monopropyl ether(PGP) there was added a solution of 0.92 g of 70% nitric acid in 65.8 gof water, dropwise over a period of 30 minutes while stirring. Aftercompletion of the dropwise addition, reaction was conducted for 5 hoursto obtain a polysiloxane solution. Next, 22.9 g of a methyl methacrylatepolymer solution was added and the produced ethanol was distilled offunder reduced pressure in a warm bath to obtain 630 g of a siloxaneresin composition 2-2.

(Production of Borazine-Based Resin Composition 2-2)

After dissolving 3.6 g (15 mmol) ofB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and 3.6 g (15 mmol)of 1,3,5,7-tetramethylcyclotetrasiloxane in 150 ml of mesitylene, 30 μlof a solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 1 day undernitrogen at 40° C. After adding an additional 30 μl of a solution ofplatinum-divinyltetramethyldisiloxane in xylene (2% platinum content),the mixture was further stirred for 1 day under nitrogen at 40° C. Next,0.36 g (1.5 mmol) of 1,3,5,7-tetramethylcyclotetrasiloxane was added andstirring was continued for 1 day under nitrogen at 40° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming disappearance of the peaks for theB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane monomers. The molecular weight ofthe product as determined by GPC analysis (based on standardpolystyrene) was Mn=11,000 (Mw/Mn=29).

After then adding 1.0 g of metal scavengers of formula (9)(3-mercaptopropyl-functionalized silica gel, product of Aldrich) to thereaction solution, it was stirred at room temperature for 2 hours. Theplatinum-adsorbed metal scavengers were filtered out on a PTFE membranefilter by ADVANTEC to obtain a borazine-based resin composition 2-2according to the invention.

(Formation of Composite Insulating Film 2-2)

First, the siloxane resin composition 2-2 was passed through a filterand spin coated onto a low resistivity silicon wafer (resistivity <10Ωcm) at 2000 rpm/30 sec. The solvent was then removed at 150° C./1min+250° C./1 min to form a first insulating film. This was followed byspin coating of the borazine-based resin composition 2-2 at 1000 rpm/30sec. The solvent was then removed at 200° C./10 min to form a secondinsulating film. The wafer was subjected to 400° C./30 min in a quartztube furnace with the O₂ concentration controlled to about 100 ppm forfinal curing of both insulating films, to obtain a composite insulatingfilm 2-2 of the invention.

Comparative Example 2-1

The siloxane resin composition produced in Example 2-1 was passedthrough a filter and spin coated at 2000 rpm/30 sec. After the spincoating, the solvent was removed at 150° C./1 min+250° C./1 min to forma film. The wafer was then subjected to 400° C./30 min in a quartz tubefurnace with the O₂ concentration controlled to about 100 ppm for finalcuring of the film, to obtain a comparison insulating film 2-3 composedof a single layer.

<Measurement of Specific Dielectric Constant>

The specific dielectric constants of composite insulating films 2-1 and2-2 obtained in Examples 2-1 and 2-2 and the insulating film 2-3obtained in Comparative Example 2-1 were measured. The definition andmethod of determining the “specific dielectric constant” were the sameas for measurement of the film thickness of the insulating film.

<Measurement of Young's Modulus>

The Young's modulus of each insulating film was measured in the samemanner as above, as an index of the film strength.

<Evaluation of CMP Resistance>

After laminating a P-TEOS film to 0.1 μm on each insulating film by CVD,Ta metal was laminated to 0.03 μm and Cu metal was laminated to 0.2 μmby sputtering. Each insulating film was then subjected to CMP polishingunder conditions normally expected to avoid polishing of the insulatingfilm (conditions for polishing of only the Cu). The slurry used wasHS-C430 by Hitachi Kasei Kogyo Co., Ltd., and the polishing was carriedout for 1 minute with an applied load of 400 gf/cm². Since the CMPconditions were such that only the Cu was polished, residue of the Tametal on the film surface after polishing indicated no interfacialpeeling between the films. Samples with a Ta metal surface remaining onthe entire surface were evaluated as “∘”, and samples in whichinterfacial peeling between the films was observed or cohesive failureoccurred due to inadequate film strength were evaluated as x

Table 3 shows the evaluation results for the specific dielectricconstant, Young's modulus and CMP resistance for each of the compositeinsulating films 2-1 and 2-2 and the insulating film 2-3. TABLE 3Specific Young's dielectric modulus CMP constant (−) (GPa) resistanceComposite insulating 2.4 9 ◯ film 2-1 (Example 2-1) Composite insulating2.3 8 ◯ film 2-2 (Example 2-2) Insulating film 2-3 2.4 7 X (Comp. Ex.2-1)

Example 3-1

(Production of Borazine-Based Resin Composition 3-1)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.1 g (0.50 mmol) ofp-bis(dimethylsilyl)benzene in 4 ml of ethylbenzene, 0.4 g of 5%platinum-alumina (0.1 mmol as platinum) was added as a supportedcatalyst having the catalyst supported on a compound-based carrier, andthe mixture was stirred for 7 days under nitrogen at 50° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming almost complete disappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers.

FIG. 3 is a graph showing a gas chromatogram of the reaction solutionimmediately after start of polymerization, and FIG. 4 is a graph showinga gas chromatogram of the reaction solution after 3 days of stirringfrom the start of polymerization. The letter “a” in FIG. 3 indicates thepeak corresponding to p-bis(dimethylsilyl)benzene, and the letters “b”in FIGS. 3 and 4 indicate the peak corresponding toB,B′,B″-triethynyl-N,N′,N″-trimethylborazine.

The molecular weight of the product as determined by GPC analysis (basedon standard polystyrene) was Mn=2500 (Mw/Mn=2.0). FIG. 5 is a graphshowing a GPC chart for the polymer. The reaction solution containingthe platinum-alumina catalyst was filtered with a disposable membranefilter unit by ADVANTEC (filter mean pore size: 0.5 μm) to obtain aborazine-based resin composition 3-1.

Example 3-2

(Production of Borazine-Based Resin Composition 3-2)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.12 g (0.50 mmol) of1,3,5,7-tetramethylcyclotetrasiloxane in 4 ml of ethylbenzene, 0.4 g of5% platinum-alumina (0.1 mmol as platinum) was added as a supportedcatalyst having the catalyst supported on a compound-based carrier, andthe mixture was stirred for 7 days under nitrogen at 50° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming almost complete disappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine monomer. The molecularweight of the product as determined by GPC analysis (based on standardpolystyrene) was Mn=3000 (Mw/Mn=2.2). The reaction solution containingthe platinum-alumina catalyst was filtered with a disposable membranefilter unit by ADVANTEC (filter mean pore size: 0.5 μm) to obtain aborazine-based resin composition 3-2.

Example 3-3

(Production of Borazine-Based Resin Composition 3-3)

A borazine-based resin composition 3-3 was obtained by the same methodas in Example 3-1, except for using the polymer-supported platinumcatalyst (polym-CH₂SH/H₂PtCl₆) described in Polymer Journal, 34,97-102(2002) (0.01 mmol as platinum) as a supported catalyst having thecatalyst supported on a compound-based carrier.

Example 3-4

A borazine-based resin composition was obtained by the same method asExample 3-1, except for using a platinum-carbon catalyst (a catalystsupported on a carbon-based carrier) as a solid catalyst. Uponfiltration with a disposable membrane filter unit by ADVANTEC (filtermean pore size: 0.5 μm), residue of the platinum-carbon catalyst wasfound in the filtrate, and therefore filtration was carried out againwith the unit using a filter mean pore size of 0.2 μm, to obtain aborazine-based resin composition 3-4.

Comparative Example 3-1

(Production of Borazine-Based Resin Composition 3-5)

After dissolving 0.50 mmol ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.50 mmol ofp-bis(dimethylsilyl)benzene in 8 ml of ethylbenzene, 10 μl of a solutionof the homogeneous metal catalyst platinum-divinyltetramethyldisiloxanein xylene (2% platinum content) was added and the mixture was stirredfor 3 days under nitrogen at room temperature. A portion of the reactionsolution was sampled and analyzed by gas chromatography (GC), confirmingdisappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene monomers. The molecular weight of theproduct as determined by GPC analysis (based on standard polystyrene)was Mn=4300 (Mw/Mn=2.5). The reaction solution was used as theborazine-based resin composition 3-5.

Example 3-5

(Production of Insulating Film 3-1)

The borazine-based resin composition 3-1 obtained in Production Example3-1 was filtered through a filter and the filtrate was added dropwiseonto a low resistivity silicon wafer (substrate; resistivity <10 Ωcm)for spin coating. The silicon wafer was then heated for 1 hour on a hotplate at 200° C. in a nitrogen atmosphere, and then baked at 300° C. for30 minutes and at 400° C. for 30 minutes, to obtain an insulating film3-1 of the invention.

Example 3-6

(Production of Insulating Film 3-2)

An insulating film 3-2 of the invention was obtained in the same manneras Example 3-5, except that the borazine-based resin composition 3-2obtained in Example 3-2 was used instead of the borazine-based resincomposition 3-1.

Example 3-7

(Production of Insulating Film 3-3)

An insulating film 3-3 of the invention was obtained in the same manneras Example 3-5, except that the borazine-based resin composition 3-3obtained in Example 3-3 was used instead of the borazine-based resincomposition 3-1.

Example 3-8

(Production of Insulating Film 3-4)

An insulating film 3-4 of the invention was obtained in the same manneras Example 3-5, except that the borazine-based resin composition 3-4obtained in Example 3-4 was used instead of the borazine-based resincomposition 3-1.

Comparative Example 3-2

(Production of Insulating Film 3-5)

An insulating film 3-5 of the invention was obtained in the same manneras Example 3-5, except that the borazine-based resin composition 3-5obtained in Comparative Example 3-1 was used instead of theborazine-based resin composition 3-1.

Example 3-9

(Production of Borazine-Based Resin Composition 3-6)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and 0.12 g (0.50mmol) of 1,3,5,7-tetramethylcyclotetrasiloxane in 4 ml of ethylbenzene,0.4 g of 5% platinum-alumina (0.1 mmol as platinum) was added as asupported catalyst having the catalyst supported on a compound-basedcarrier, and the mixture was stirred for 7 days under nitrogen at 50° C.A portion of the reaction solution was sampled and analyzed by gaschromatography (GC), confirming almost complete disappearance of thepeaks for the B,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane monomers. The molecular weight ofthe product as determined by GPC analysis (based on standardpolystyrene) was Mn=7000 (Mw/Mn=5.0). The reaction solution containingthe platinum-alumina catalyst was filtered with a disposable membranefilter unit by ADVANTEC (filter mean pore size: 0.5 μm) to obtain aborazine-based resin composition 3-6.

Example 3-10

(Production of Insulating Film 3-6)

An insulating film 3-6 of the invention was obtained in the same manneras Example 3-5, except that the borazine-based resin composition 3-6obtained in Example 3-9 was used instead of the borazine-based resincomposition 3-1.

<Measurement of Specific Dielectric Constant>

The specific dielectric constants of each of the insulating filmsobtained in the examples and comparative examples were measured. Thedefinition and method of determining the “specific dielectric constant”were the same as for measurement of the film thickness of the insulatingfilm.

Table 4 shows the platinum contents for borazine-based resincompositions 3-1 to 3-3, 3-5 and 3-6. The platinum contents weredetermined by acid decomposition of a fixed amount of sample andmeasurement with a model SPQ9000 ICP-MS by Seiko Instruments. Table 5shows the results of measuring the specific dielectric constants andleak current values for the insulating films 3-1 to 3-3, 3-5 and 3-6.TABLE 4 Platinum concentration Resin composition (ppm) 3-1 (Example 3-1)2 3-2 (Example 3-2) 1 3-3 (Example 3-3) 5 3-5 (Comp. Ex. 3-1) 34 3-6(Example 3-9) 1

TABLE 5 Specific dielectric constant Leak current Insulating film (−)(A/cm²) 3-1 (Example 3-5) 2.1 1 × 10⁻¹⁰ 3-2 (Example 3-6) 2.1 1 × 10⁻¹⁰3-3 (Example 3-7) 2.2 2 × 10⁻¹⁰ 3-5 (Comp. Ex. 3-2) 2.5 8 × 10⁻¹⁰ 3-6(Example 3-10) 2.2 2 × 10⁻¹⁰

Table 4 demonstrates that the metal impurity (platinum) contents of theborazine-based resin compositions 3-1 to 3-3 and 3-6 which employedsupported catalysts as the polymerization catalysts were drasticallyreduced compared to the untreated composition (the borazine-based resincomposition 3-5 obtained in the comparative example). Table 5demonstrates that the specific dielectric constants and leak currents ofthe insulating films 3-1 to 3-3 and 3-6 which were formed, respectively,by the borazine-based resin compositions 3-1 to 3-3 and 3-6 having lowmetallic impurity contents, were adequately reduced compared to theinsulating film 3-5 formed by the borazine-based resin composition 3-5.

Example 4-1

(Production of Borazine-Based Resin Composition 4-1)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.1 g (0.50 mmol) ofp-bis(dimethylsilyl)benzene in 8 ml of ethylbenzene, 10 μl of a solutionof platinum-divinyltetramethyldisiloxane in xylene (2% platinum content)was added and the mixture was stirred for 3 days under nitrogen at roomtemperature. A portion of the reaction solution was sampled and analyzedby gas chromatography (GC), confirming almost complete disappearance ofthe peak for the B,B′,B″-triethynyl-N,N′,N″-trimethylborazine monomerand complete disappearance of the peak for thep-bis(dimethylsilyl)benzene monomer.

FIG. 6 is a graph showing a gas chromatogram of the reaction solutionimmediately after start of polymerization, and FIG. 7 is a graph showinga gas chromatogram of the reaction solution after 3 days of stirringfrom the start of polymerization. The letter “a” in FIG. 6 indicates thepeak corresponding to p-bis(dimethylsilyl)benzene, and the letters “b”in FIGS. 6 and 7 indicate the peak corresponding toB,B′,B″-triethynyl-N,N′,N″-trimethylborazine.

The molecular weight of the product as determined by GPC analysis (basedon standard polystyrene) was Mn=4300 (Mw/Mn=2.5). FIG. 8 is a graphshowing a GPC chart for the polymer. After then adding 0.2 g of metalscavengers represented by formula (10)(3-(diethylenetriamino)propyl-functionalized silica gel, product ofAldrich) to the reaction solution, it was stirred at room temperaturefor 2 hours. The platinum-adsorbed metal scavengers were then filteredout with a disposable membrane filter unit by ADVANTEC to obtain aborazine-based resin composition 4-1 according to the invention.

Example 4-2

(Production of Borazine-Based Resin Composition 4-2)

In the same manner as Example 4-1,B,B′,B″-triethynyl-N,N′,N″-trimethylborazine andp-bis(dimethylsilyl)benzene were polymerized in the presence ofplatinum-divinyltetramethyldisiloxane. After then adding 0.2 g of metalscavengers of formula (9) (3-mercaptopropyl-functionalized silica gel,product of Aldrich) to the reaction solution, it was stirred at roomtemperature for 2 hours. The platinum-adsorbed metal scavengers werefiltered out with a disposable membrane filter unit by ADVANTEC toobtain a borazine-based resin composition 4-2 according to theinvention.

Example 4-3

(Production of Borazine-Based Resin Composition 4-3)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.12 g (0.50 mmol) of1,3,5,7-tetramethylcyclotetrasiloxane in 8 ml of ethylbenzene, 10 μl ofa solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 3 days undernitrogen at room temperature. A portion of the reaction solution wassampled and analyzed by gas chromatography (GC), confirmingdisappearance of the peaks for theB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane monomers.

The molecular weight of the product as determined by GPC analysis (basedon standard polystyrene) was Mn=4500 (Mw/Mn=2.6). After then adding 0.2g of metal scavengers represented by formula (8)(3-(diethylenetriamino)propyl-functionalized silica gel, product ofAldrich) to the reaction solution, it was stirred at room temperaturefor 2 hours. The platinum-adsorbed metal scavengers were then filteredout with a disposable membrane filter unit by ADVANTEC to obtain aborazine-based resin composition 4-3 according to the invention.

Example 4-4

(Production of Borazine-Based Resin Composition 4-4)

In the same manner as Example 4-1,B,B′,B″-triethynyl-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane were polymerized in the presenceof platinum-divinyltetramethyldisiloxane. After then adding 0.2 g ofmetal scavengers of formula (9) (3-mercaptopropyl-functionalized silicagel, product of Aldrich) to the reaction solution, it was stirred atroom temperature for 2 hours. The platinum-adsorbed metal scavengerswere filtered out with a disposable membrane filter unit by ADVANTEC toobtain a borazine-based resin composition 4-4 according to theinvention.

Example 4-5

(Production of Borazine-Based Resin Composition 4-5)

After dissolving 3.6 g (15 mmol) ofB,B′,B″-tris(1-propynyl)-N,N′,N″-trimethylborazine and 3.6 g (15 mmol)of 1,3,5,7-tetramethylcyclotetrasiloxane in 150 ml of mesitylene, 30 lof a solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 1 day undernitrogen at 40° C. After adding an additional 30 μl of a solution ofplatinum-divinyltetramethyldisiloxane in xylene (2% platinum content),the mixture was further stirred for 1 day under nitrogen at 40° C. Next,0.36 g (1.5 mmol) of 1,3,5,7-tetramethylcyclotetrasiloxane was added andstirring was continued for 1 day under nitrogen at 40° C. A portion ofthe reaction solution was sampled and analyzed by gas chromatography(GC), confirming disappearance of the peaks for theB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and1,3,5,7-tetramethylcyclotetrasiloxane monomers.

FIG. 9 is a graph showing a GPC chart for the obtained polymer. Themolecular weight of the product as determined by GPC analysis (based onstandard polystyrene) was Mn=11,000 (Mw/Mn=29).

After then adding 1.0 g of metal scavengers of formula (9)(3-mercaptopropyl-functionalized silica gel, product of Aldrich) to thereaction solution, it was stirred at room temperature for 2 hours. Theplatinum-adsorbed metal scavengers were filtered out on a PTFE membranefilter by ADVANTEC to obtain a borazine-based resin composition 4-5according to the invention.

Comparative Example 4-1

(Production of Borazine-Based Resin Composition 4-6)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.1 g (0.50 mmol) ofp-bis(dimethylsilyl)benzene in 8 ml of ethylbenzene, 10 μl of a solutionof the homogeneous metal catalyst platinum-divinyltetramethyldisiloxanein xylene (2% platinum content) was added and the mixture was stirredfor 3 days under nitrogen at room temperature. The reaction solution wasused as the borazine-based resin composition 4-6.

Comparative Example 4-2

(Production of Borazine-Based Resin Composition 4-7)

After dissolving 0.1 g (0.50 mmol) ofB,B′,B″-triethynyl-N,N′,N″-trimethylborazine and 0.12 g (0.50 mmol) of1,3,5,7-tetramethylcyclotetrasiloxane in 8 ml of ethylbenzene, 10 μl ofa solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 3 days undernitrogen at room temperature. The reaction solution was used as theborazine-based resin composition 4-7.

Comparative Example 4-3

(Production of Borazine-Based Resin Composition 4-8)

After dissolving 1.2 g (5 mmol) ofB,B′,B″-tris(1′-propynyl)-N,N′,N″-trimethylborazine and 1.2 g (5 mmol)of 1,3,5,7-tetramethylcyclotetrasiloxane in 50 ml of mesitylene, 10 μlof a solution of platinum-divinyltetramethyldisiloxane in xylene (2%platinum content) was added and the mixture was stirred for 1 day undernitrogen at 40° C. After then adding an additional 10 μl of a solutionof platinum-divinyltetramethyldisiloxane in xylene (2% platinumcontent), the mixture was further stirred for 1 day under nitrogen at40° C. Next, 0.12 g (0.5 mmol) of 1,3,5,7-tetramethylcyclotetrasiloxanewas added and stirring was continued for 1 day under nitrogen at 40° C.The reaction solution was used as the borazine-based resin composition4-8.

Comparative Example 4-6

(Production of Borazine-Based Resin Composition 4-1)

The borazine-based resin composition 4-1 obtained in Production Example4-1 was filtered through a filter and the filtrate was added dropwiseonto a low resistivity silicon wafer (substrate; resistivity <10 Ωcm)for spin coating. The silicon wafer was then heated for 1 hour on a hotplate at 200° C. in a nitrogen atmosphere, and then baked at 300° C. for30 minutes and at 400° C. for 30 minutes, to obtain an insulating film4-1 of the invention.

Example 4-7

(Production of Insulating Film 4-2)

An insulating film 4-2 of the invention was obtained in the same manneras Example 4-6 except that the borazine-based resin composition 4-2obtained in Example 4-2 was used instead of the borazine-based resincomposition 4-1.

Example 4-8

(Production of Insulating Film 4-3)

An insulating film 4-3 of the invention was obtained in the same manneras Example 4-6 except that the borazine-based resin composition 4-3obtained in Example 4-3 was used instead of the borazine-based resincomposition 4-1.

Example 4-9

(Production of Insulating Film 4-4)

An insulating film 4-4 of the invention was obtained in the same manneras Example 4-6 except that the borazine-based resin composition 4-4obtained in Example 4-4 was used instead of the borazine-based resincomposition 4-1.

Example 4-10

(Production of Insulating Film 4-5)

An insulating film 4-5 of the invention was obtained in the same manneras Example 4-6 except that the borazine-based resin composition 4-5obtained in Example 4-5 was used instead of the borazine-based resincomposition 4-1.

Comparative Example 4-4

(Production of Insulating Film 4-6)

An insulating film 4-6 was obtained in the same manner as Example 4-6except that the borazine-based resin composition 4-6 obtained inComparative Example 4-1 was used instead of the borazine-based resincomposition 4-1.

Comparative Example 4-5

(Production of Insulating Film 4-7)

An insulating film 4-7 was obtained in the same manner as Example 4-6except that the borazine-based resin composition 4-7 obtained inComparative Example 4-2 was used instead of the borazine-based resincomposition 4-1.

Comparative Example 4-6

(Production of Insulating Film 4-8)

An insulating film 4-8 was obtained in the same manner as Example 4-6except that the borazine-based resin composition 4-8 obtained inComparative Example 4-3 was used instead of the borazine-based resincomposition 4-1.

<Measurement of Specific Dielectric Constant>

The specific dielectric constants of each of the composite insulatingfilms obtained in the examples and comparative examples were measured.The definition and method of determining the “specific dielectricconstant” were the same as for measurement of the film thickness of theinsulating film.

Table 6 shows the platinum contents for borazine-based resincompositions 4-1 to 4-8. The platinum contents were determined by aciddecomposition of a fixed amount of sample and measurement with a modelSPQ9000 ICP-MS by Seiko Instruments. Table 7 shows the results ofmeasuring the specific dielectric constants and leak current values forthe insulating films 4-1 to 4-8. TABLE 6 Borazine-based resin Platinumconcentration composition (ppm) 4-1 (Example 4-1) 5 4-2 (Example 4-2) 34-3 (Example 4-3) 5 4-4 (Example 4-4) 4 4-5 (Example 4-5) 2 4-6 (Comp.Ex. 4-1) 31 4-7 (Comp. Ex. 4-2) 33 4-8 (Comp. Ex. 4-3) 32

TABLE 7 Specific dielectric constant Leak current Insulating film (−)(A/cm²) 4-1 (Example 4-6) 2.3 3 × 10⁻¹⁰ 4-2 (Example 4-7) 2.2 2 × 10⁻¹⁰4-3 (Example 4-8) 2.3 3 × 10⁻¹⁰ 4-4 (Example 4-9) 2.2 2 × 10⁻¹⁰ 4-5(Example 4-10) 2.3 1 × 10⁻¹⁰ 4-6 (Comp. Ex. 4-4) 2.5 8 × 10⁻¹⁰ 4-7(Comp. Ex. 4-5) 2.6 9 × 10⁻¹⁰ 4-8 (Comp. Ex. 4-6) 2.5 9 × 10⁻¹⁰

Table 6 demonstrates that the platinum contents of the borazine-basedresin compositions 4-1 to 4-5 which had been subjected to metalscavenger treatment after polymerization were drastically reducedcompared to the untreated compositions (the borazine-based resincompositions 4-6 to 4-8 obtained in the comparative examples). Table 7demonstrates that the specific dielectric constants and leak currents ofthe insulating films 1 to 5 which were formed, respectively, by theborazine-based resin compositions 4-1 to 4-5 having low metallicimpurity contents, were adequately reduced compared to the insulatingfilms 4-6 to 4-8 formed by the borazine-based resin compositions 4-6 to4-8.

INDUSTRIAL APPLICABILITY

According to the insulating film A of the invention, the dielectricconstant is adequately reduced to result in excellent electricalcharacteristics, while the lower dielectric constant does not requirepore formation so that the mechanical strength can be sufficientlyincreased. Furthermore, since electronic parts A according to theinvention are provided with an insulating film according to theinvention, it is possible to effectively prevent wiring delay whileenhancing mechanical strength and reliability.

A composite insulating film or electronic part B according to theinvention has a second insulating film composed of a compound with aborazine skeleton in the molecular structure on a first insulating filmcomposed of a siloxane resin, and it is therefore possible to achieve anadequately low dielectric constant, increase the mechanical strength anddrastically improve adhesion with upper layer films, while alsoenhancing peel resistance against polishing by CMP or the like (CMPresistance).

According to the first and second borazine-based resin productionprocesses, the borazine-based resin and the borazine-based resincomposition of the invention, it is possible to form insulating filmshaving low metallic impurities and satisfactorily inhibited leakcurrent. Also, an insulating film and its production process accordingto the invention, based on the first and second borazine-based resinproduction processes, allow leak current to be satisfactorily inhibitedwhile enhancing properties such as heat resistance. In addition, anelectronic part C according to the invention also has satisfactorilyinhibited leak current and adequately prevents reduction ordeterioration of characteristics.

1. An insulating film comprising a compound having a borazine skeletonin a molecular structure thereof, and having a specific dielectricconstant of no greater than 2.6, a Young's modulus of 5 GPa or greaterand a leak current of no greater than 1×10⁻⁸A/cm².
 2. An insulating filmaccording to claim 1, wherein the insulating film is formed from aborazine-based resin composition with a metal impurity content of nogreater than 30 ppm.
 3. An electronic part provided with a conductivelayer-formed substrate and an interlayer insulating film formed on thesubstrate, wherein the interlayer insulating film is composed of aninsulating film according to claim
 1. 4. A composite insulating filmcomprising: a first insulating film comprising a siloxane resin, and asecond insulating film formed on the first insulating film andcomprising a compound having a borazine skeleton in a molecularstructure thereof.
 5. A composite insulating film according to claim 4,wherein the first insulating film is composed of a siloxane resincomposition comprising a siloxane resin obtained by hydrolyticcondensation of a compound represented by the following formula (1):X ¹ _(n)SiX² _(4-n)   (1) where X¹ represents an H atom, an F atom, agroup containing a B atom, N atom, Al atom, P atom, Si atom, Ge atom orTi atom, or an organic group of 1 to 20 carbons, X² represents ahydrolyzable group, and n represents an integer of 0-2, with the provisothat when n is 2, each X¹ may be the same or different, and when n is0-2, each X² may be the same or different.
 6. A composite insulatingfilm according to claim 4, wherein the compound having a borazineskeleton in a molecular structure thereof has a repeating unitrepresented by the following formula (2):

where R¹ represents alkyl, aryl, aralkyl or hydrogen, R² representsalkyl, aryl, aralkyl or hydrogen, R³ and R⁴ represent identical ordifferent monovalent groups selected from among alkyl, aryl, aralkyl andhydrogen, R⁵ represents a substituted or unsubstituted aromatic divalentgroup, an oxypoly (dimethylsiloxy) group or oxygen, R⁶ represents alkyl,aryl, aralkyl or hydrogen, a represents a positive integer, b represents0 or a positive integer, p represents 0 or a positive integer, and qrepresents 0 or a positive integer.
 7. An electronic part provided witha composite insulating film according to claim 4, wherein the compositeinsulating film is formed on a substrate.
 8. A process for production ofa borazine-based resin that is a polymer having a borazine skeleton on amain chain or a side chain thereof, wherein the process comprises: afirst step of polymerizing a B,B′,B″-trialkynylborazine and ahydrosilane in the presence of a solid catalyst, and a second step ofremoving the solid catalyst after completing the first step.
 9. Aprocess for production of a borazine-based resin according to claim 8,wherein the solid catalyst is a supported catalyst comprising a catalystsupported on compound-based carrier.
 10. A process for production of aborazine-based resin that is a polymer having a borazine skeleton on amain chain or a side chain thereof wherein the process comprises: afirst step of polymerizing a B,B′,B″-trialkynylborazine and ahydrosilane in the presence of a metal catalyst in a polymerizationsolvent, a second step of adding to the polymerization system aparticulate scavenger which is insoluble in the polymerization system ofthe first step and adsorbs the metal component from the metal catalyst,after completion of the first step, and a third step of filtering outthe scavenger to which the metal component has been adsorbed aftercompletion of the second step.
 11. A process for production of aborazine-based resin according to claim 8, wherein theB,B′,B″-triallcynylborazine is represented by the following formula (3):

where R¹ represents alkyl, aryl, aralkyl or hydrogen, and R² representsalkyl, aryl, aralkyl or hydrogen.
 12. A process for production of aborazine-based resin according to claim 8, wherein the hydrosilane isrepresented by the following formula (4):

where R³ and R⁴ represent identical or different monovalent groupsselected from among alkyl, aryl, aralkyl and hydrogen, R⁵ represents asubstituted or unsubstituted aromatic divalent group, an oxypoly(dimethylsiloxy) group or oxygen, or by the following formula (5):

where R⁶ represents alkyl, aryl, aralkyl or hydrogen, and n representsan integer of 2 or greater.
 13. A borazine-based resin compositioncomprising a polymer with a borazine skeleton on a main chain or a sidechain thereof, and a solvent capable of dissolving the polymer, andhaving a solid concentration of 0.5 wt % or greater and a metal impuritycontent of no greater than 30 ppm.
 14. A borazine-based resincomposition comprising a polymer with a borazine skeleton on a mainchain or a side chain thereof. and a solvent capable of dissolving thepolymer, and having a solid concentration of 0.5 wt % or greater and ametal impurity content of no greater than 30 ppm, wherein the polymer isa borazine-based resin produced by a borazine-based resin productionprocess according to claim
 8. 15. A borazine-based resin compositionaccording to claim 13, wherein the polymer has a repeating unitrepresented by the following formula (2):

where R¹ represents alkyl, aryl, aralkyl or hydrogen, R² representsalkyl, aryl, aralkyl or hydrogen, R³ and R⁴ represent identical ordifferent monovalent groups selected from among alkyl, aryl, aralkyl andhydrogen, R⁵ represents a substituted or unsubstituted aromatic divalentgroup, an oxypoly(dimethylsiloxy) group or oxygen, R⁶ represents alkyl,aryl, aralkyl or hydrogen, a represents a positive integer, b represents0 or a positive integer, p represents 0 or a positive integer, and qrepresents 0 or a positive integer.
 16. A method for forming aninsulating film on a substrate, wherein a borazine-based resincomposition according to claim 13 is coated onto the substrate to form acoated film, and the coated film is then dried.
 17. An insulating filmprovided on a substrate, the insulating film being formed by a methodfor forming an insulating film according to claim
 16. 18. An insulatingfilm according to claim 17, wherein the insulating film is formedbetween mutually adjacent conductive layers among a plurality ofconductive layers provided on the substrate.
 19. An electronic partcomprising an insulating film according to claim
 17. 20. Aborazine-based resin produced by a borazine-based resin productionprocess according to claim 8.